Slangs

yack (!)    Exclam. An exclamation of disgust. A variation on 'yuck!'.
Verb. To talk incessantly and boringly. Also spelt yak and often extended to yack on, meaning the same.
yack up   Verb. To vomit. E.g."That was the worst meal ever; I feel like yacking up."
yacky    Adj. Disgusting, vile.
yam   Noun. Home. Also 'yem'. [North-east/Cumbrian use. Dialect?]
yampy   Adj. Crazy, mad, insane. [Birmingham/ W. Midlands use]
yam yam   Noun. A person from the Black Country, an area of England encompassing Wolverhampton, Dudley, and Stourbridge. From the way in which people from this locality speak. Derog. [Birmingham use]
yank    Noun. An act of masturbation. Male usage. E.g."Oh God! I just walked in on Martin having a yank."
Verb. To masturbate. E.g."He looks like he's been up all night yanking."
yap    Verb. To talk incessantly. {Informal}
yard   Noun. One's home. [London use]
yardie   Noun. A member of a Jamaican criminal gang. Usually operating internationally and in the distribution of illicit drugs. [Jamaica]
ya wank    Noun. A contemptible person. [Scottish use]
yawn    Noun. Something that is very boring. E.g."Amanda's boyfriend is obsessed with football, he's such a yawn." {Informal}
y-bone steak   Noun. The female genitals.
yellow belly    Noun. A person from Lincolnshire.
yem   Noun. See 'yam'.
yikes!    Exclam. An expression of surprise or astonishment.
yitney   Noun. A coward. Also yitni. [Notts. & Leics. use/Dialect?]
yo!    Exclam. A greeting or an attention seeking call. [Orig. U.S.]
yob    Noun. A lout or hooligan. Derived from the backslang of boy.
yobbo    Noun. Meaning the same as 'yob'.
yomp    Verb. To walk hard and with vigour. [1900s]
yonks    Noun. An age, a long time.
you're having a laugh (!)   Phrs./Exclam. See 'having a laugh'.
yoursen   Pron. Yourself. [Northern use/Dialect]
yo-yo knickers   Noun. A promiscuous woman, a sexually loose woman. From the frequency of her underwear going up and down. Derog.
yuck (!)    Noun. A thing that is vile or distasteful. E.g."Don't eat that, it's yuck and tastes mouldy."
Exclam. Expressing extreme distaste.
yucky    Adj. Very unpleasant or distasteful.