When you are at a party with your friends and you feel like fucking around. Walk up to a random girl, and ask her "Yay or Nay?" She will either respond with a "Yay", in which case you will proceed to hook up (make-out), or a "Nay", where you will feel brutally defeated.
Micah: Yo Adam, pull a yay or nay on that girl over there.
Adam: Nah brother, she'll say no.
Micah: Brother, stop being a bitch and do it.
(Walking up to random girl)
Adam: Yay or Nay, we hook up right now.
Hot Girl: YAY
When someone is required to make an important decision or they are interested in someone's opinion on a matter, they will often ask the question "Hey Buddy (insert object here) Yay or Nay?" The answer "Yay" would imply that the person fully supports the cause, while a simple "Nay" would do just the opposite.
Rhyming Alternatives to Yay and Nay:
Gay! - Used when the object or the person asking the question is quite homosexual.
Bay! - Used when near a harbor.
Hay! - Used when you're really in that "LAWL HORSES" mood. Gotta love horses.
K. - Used when you're really not interested in the question.
Guy 1: Boobs, Yay or Nay?
Guy 2: YAY!
Guy 1: Ann Coulter, Yay or Nay!?
Guy 2: FUCK THAT BITCH. NAY!
Guy 1: Getting blown by babes ten times in the last four days, Yay or Nay?
Guy 2: Gay.
Guy 1: WHAT!?
Guy 2: Seriously, faggot, get out of my sight.