Vegan Booty; Phrase, a persons backside that does not contain much meat/fat/flesh. An undesirable buttocks due to lack of size.
"Yo she got that vegan booty, she needs to eat something!", "Man, after his diet dude rocking that vegan booty, you know his boyfriend don't like that!"
More intellectual equivalent of saying dat ass in which saying it by itself is most often sufficient with a look in the general direction.
Guy A: Yo man, rtb!
Guy B: Yeah, at first I just gave that girl at the club an rts but now, you're right, after a few drinks and after seeing her twerk all night, I came to respect that booty.
Remember kids, if you're an ass man: rtsb+rt^2=rte, rte>rtsb>rtb>rt^2>rts