yet another def...
In military terms, most especially the Navy, merkin is pubic hair left behind on either a toilet seat, or the rim of a men's urinal. More closely associated to women's restrooms than to men's, but applies to both.
A source of great consternation for those assigned the task of 'cleaning the head(restroom)'.
Jay - "Dude, check out all this fucking merkin on the shitter seat!"
Bob - "Thats foul bro! I aint cleaning that up... its your turn!"
Acronym for 'You Are Fucking Me Again'. Used as an imperative when the user has discovered some real or perceived woe exacted upon them by another.
Originates from military vernacular, but has proliferated into some civilian circles.
Joe - "Ed, I just told our section manager about how you surf porn on your terminal at lunchtime."
Ed - "Yafma."