Derived from the word transmission, when a car's transmission breaks down, but is not limited to that. If a car has a flat tire, or is not drivable, then it dropped a tranny.
Jim: Are you coming over to my house tonight?
Mike: Yeah, as long as my car doesn't drop a tranny.
1. Phrase; when driving, one's transmission unexpectedly falls out.
2. Phrase; a freakish sexual act when the following occurs: one has sexual intercourse with a transvestite on top of a tall building; immediately following one's orgasm, one unexpectedly throws said transvestite off the building; one jumps after her/him/it; and uses her/him/it to break one's fall. Then walk away unscathed with great story for one's drinking buddies.
This is the sort of thing that, I'll bet, happens to too many guys in the East Village. Next time some super hot "chick" hits on you, be suspicious by all means, then go back to her place with her, ask to go up to the roof because "it'll be more romantic," then drop a tranny.