to be the next or newest big thing. it comes from a double reference: it is a bastardization of "on point" which means on top of things, with a baseball on-deck circle. in baseball, the on deck circle is where the next batter stands while he waits for his turn to bat. hence, the next big thing is "on deck."
1. yo, those boots are booty.
2. nah, man, these are on deck.