to put something in your ass. usually reserved for concealing illegal substances from authority, it can also mean to introduce illegal substances into the bloodstream with the quickness.
"i saw these kids at a rave, and they were taking E and bootin it! they got 10 times higher, 10 times quicker!"
purging after a long night of binging
C- Where's H?
J- I think she's bootin it after drinking like 5 beers!?!
C- What a candy-ass!