Ugliest words in English

You may be thinking these are words to avoid in your writing but don't be so quick to exclude them. There are many perfect for children's books, especially those to do with bodily functions. Others can be used specifically to heighten the tension or negative reaction a reader will feel. They could ruin a poetic piece if used incorrectly or they could make a story by highlighting the difference between good and bad situations, pleasant and unpleasant surrounds etc. The key is to use them wisely.

• Bunion: a painful swelling on the first joint of the big toe.
• C-word: a woman’s genitals, an unpleasant or stupid person.
• Cacophony: a harsh discordant mixture of sounds
• Cataclysm: a large-scale and violent event in the natural world, a sudden violent political or social upheaval.
• Chafe: with reference to a part of the body) make or become sore by rubbing against something, [no object] (of an object) rub abrasively against another, [with object] rub (a part of the body) to restore warmth or sensation, become or make annoyed or impatient because of a restriction or inconvenience,
• Chunk: a thick, solid piece of something, (in psychology or linguistic analysis) group together (connected items or words) so that they can be stored or processed as single concepts.
• Coarse: rough or harsh in texture, (of a person or their speech) rude or vulgar, British relating to the sport of angling for coarse fish.
• Cockroach: a beetle-like scavenging insect with long antennae and legs. Several tropical kinds have become established worldwide as household pests.
• Crepuscular: resembling or relating to twilight.
• Crotch: the part of the human body between the legs where they join the torso, a fork in a tree, road, or river.
• Crunch: crush (a hard or brittle foodstuff) with the teeth, making a loud but muffled grinding sound, (especially of a computer) process (large quantities of information), [usually in singular] a loud muffled grinding sound like that of something hard or brittle being crushed, (the crunch) a crucial point or situation, typically one at which a decision with important consequences must be made, a physical exercise designed to strengthen the abdominal muscles; a sit-up.
• Curdle: separate or cause to separate into curds or lumps,
• Cynical: believing that people are motivated purely by self-interest; distrustful of human sincerity or integrity, concerned only with one’s own interests and typically disregarding accepted standards in order to achieve them.
• Decrepit: worn out or ruined because of age or neglect.
• Discharge: tell (someone) officially that they can or must leave, in particular, allow (a liquid, gas, or other substance) to flow out from where it has been confined, do all that is required to perform (a duty) or fulfil (a responsibility), Law: (of a judge or court) cancel (an order of a court), the action of discharging someone from a hospital or from the armed forces or police, the action of discharging a liquid, gas, or other substance, the action of doing all that is required to fulfil a responsibility or perform a duty, Law: the cancellation of an order of a court.
• Disgust: a feeling of revulsion or strong disapproval aroused by something unpleasant or offensive, cause (someone) to feel revulsion or strong disapproval.
• Fetid: smelling extremely unpleasant.
• Flatulent: suffering from or marked by an accumulation of gas in the alimentary canal.
• Grimace: an ugly, twisted expression on a person’s face, typically expressing disgust, pain, or wry amusement.
• Gripe: [no object] complain about something in a persistent, irritating way, [with object] (usually as adjective griping) affect with gastric or intestinal pain,  [with object]  grasp tightly; clutch, [with object] Nautical: secure (a boat) with gripes, a minor complaint, [mass noun] gastric or intestinal pain; colic, an act of grasping something tightly, (gripes) Nautical lashings securing a boat in its place on deck or in davits.
• Grotesque: comically or repulsively ugly or distorted, a very ugly or comically distorted figure or image, [mass noun] Printing a family of 19th century sans serif typefaces.
• Harangue: a lengthy and aggressive speech, lecture (someone) at length in an aggressive and critical manner.
• Hate: intense dislike, feel intense dislike for.
• Hirsute: hairy.
• Hoarse: (of a person’s voice) sounding rough and harsh, typically as the result of a sore throat or of shouting.
• Honk: the cry of a wild goose, make or cause to make a honk, [no object] vomit.
• Jazz: a type of music of black American origin which emerged at the beginning of the 20th century, characterised by improvisation, syncopation, and usually a regular or forceful rhythm. Brass and woodwind instruments and piano are particularly associated with jazz, although guitar and occasionally violin are also used; styles include Dixieland, swing, bebop, and free jazz.
• Juror: a member of a jury, historical a person taking an oath, especially one of allegiance.
• Leech: an aquatic or terrestrial annelid worm with suckers at both ends. Many species are bloodsucking parasites, especially of vertebrates, and others are predators, a person who extorts profit from or sponges on others, habitually exploit or rely on.
• Maladroit: inefficient or inept; clumsy.
• Mediocre: of only average quality; not very good.
• Moist: slightly wet, Medicine: marked by a fluid discharge.
• Mucus: a slimy substance, typically not miscible with water, secreted by the mucous membranes and glands of animals for lubrication, protection, etc.
• Obstreperous: noisy and difficult to control.
• Ointment: a smooth oily substance that is rubbed on the skin for medicinal purposes or as a cosmetic.
• Onus: a smooth oily substance that is rubbed on the skin for medicinal purposes or as a cosmetic.
• Ooze: [no object, with adverbial of direction] (of a fluid) slowly trickle or seep out of something,  [with object] give a powerful impression of (a quality), [mass noun] the sluggish flow of a fluid, an infusion of oak bark or other vegetable matter, used in tanning.
• Patriotism: the quality of being patriotic; vigorous support for one’s country.
• Pernickety: placing too much emphasis on trivial or minor details; fussy.
• Phlegm: the thick viscous substance secreted by the mucous membranes of the respiratory passages, especially when produced in excessive quantities during a cold.
• Phlegmatic: (of a person) having an unemotional and stolidly calm disposition.
• Plump: having a full rounded shape, shake or pat (a cushion or pillow) to adjust its stuffing and make it rounded and soft.
• Plutocrat: having a full rounded shape, shake or pat (a cushion or pillow) to adjust its stuffing and make it rounded and soft.
• Pregnant: (of a woman or female animal) having a child or young developing in the uterus, full of meaning; significant or suggestive.
• Puke: vomit.
• Pulchritude: beauty.
• Pus: a thick yellowish or greenish opaque liquid produced in infected tissue, consisting of dead white blood cells and bacteria with tissue debris and serum.
• Putrid: (of organic matter) decaying or rotting and emitting a fetid smell, very unpleasant; repulsive.
• Quaff: drink (something, especially an alcoholic drink) heartily, an alcoholic drink.
• Rancid: (of foods containing fat or oil) smelling or tasting unpleasant as a result of being old and stale: rancid meat.
• Regurgitate: bring (swallowed food) up again to the mouth.
• Repugnant: extremely distasteful; unacceptable, (repugnant to) in conflict or incompatible with.
• Repulsive: arousing intense distaste or disgust, relating to repulsion between physical objects, lacking friendliness or sympathy.
• Routine: a sequence of actions regularly followed, performed as part of a regular procedure rather than for a special reason, organize according to a routine.
• Rural: in, relating to, or characteristic of the countryside rather than the town.
• Sap: the fluid which circulates in the vascular system of a plant, consisting chiefly of water with dissolved sugars and mineral salts, gradually weaken or destroy (a person’s strength or power).
• Scab: a dry, rough protective crust that forms over a cut or wound during healing, [mass noun] mange or a similar skin disease in animals, a person or thing regarded with contempt, become encrusted or covered with a scab or scabs, act or work as a scab.
• Schmear: an underhand inducement, a smear or spread, flatter or ingratiate oneself with (someone).
• Shriek: utter a high-pitched piercing sound or words, especially as an expression of terror, pain, or excitement, a high-pitched piercing cry or sound; a scream, an exclamation mark.
• Shrill: (of a voice or sound) high-pitched and piercing, make a shrill noise, a shrill sound or cry.
• Shun: persistently avoid, ignore, or reject (someone or something) through antipathy or caution.
• Slaughter: kill (animals) for food.
• Smegma: a sebaceous secretion in the folds of the skin, especially under a man’s foreskin.
• Synergy: the interaction or cooperation of two or more organisations, substances, or other agents to produce a combined effect greater than the sum of their separate effects.
• Tax: a compulsory contribution to state revenue, levied by the government on workers' income and business profits, or added to the cost of some goods, services, and transactions, [in singular] a strain or heavy demand, impose a tax on (someone or something), make heavy demands on (someone’s powers or resources), confront (someone) with a fault or wrongdoing, examine and assess (the costs of a case).
• Treachery: betrayal of trust.
• Ugly: unpleasant or repulsive, especially in appearance, involving or likely to involve violence or other unpleasantness.
• Unctuous: excessively flattering or ingratiating; oily, (chiefly of minerals) having a greasy or soapy feel.
• Visceral: relating to the viscera, relating to deep inward feelings rather than to the intellect.
• Vomit: eject matter from the stomach through the mouth, [mass noun] matter vomited from the stomach, an emetic.

Thanks to: Oxford English Dictionary, Netscape Fun & Games, Alta, Daily Writing Tips, Six Things, Words Gone Wild.