yack or yak
intr.v. yakked, also yacked yakking, yacking yaks, yacks
To talk persistently and meaninglessly; chatter.
n.
Prolonged, sometimes senseless talk; chatter.

yack up: To vomit.

yap
v. yapped, yapping, yaps
v. intr.
1. To bark sharply or shrilly; yelp.
2. To talk noisily or stupidly; jabber.
v. tr.
To utter by yapping.
n.
1. A sharp, shrill bark; a yelp.
2. Noisy, stupid talk; jabber.
3. The mouth: Shut your yap.
4. A stupid, crude, or loud person.
yapper n.

yellow shower n: The act of urinating on a person as a means of sexual stimulation; a golden shower.

yo interj: Used as a greeting or to attract someone's attention.
[From the Danish yo for 'yes']

yob n: A rowdy, aggressive, or violent young man.
[Alteration of boy (spelled backward).]

yuck interj: Used to express rejection or strong disgust.