to latch, also known as "latching, or latchin" is to engage or participate in the art of trash talking a friend, colleague, homeboy or sworn enemy. It should be witty, funny and downright embarassing to the person you are trying to latch against.
Homeboy 1 - "Bro..that girl you brought home from the club the other night was buttt ugly tell me you aint hit?"
Homeboy 2 - "Dog you latchin? I know you aint tryna latch right now cause the last girl you hit had them sabertooth tiger teeth"
Surrounding Homeboys - "Oohohohohhohohhhhhhhh"