jit means that guy or dude or bro. And Trippin mean you said or did something crazy. Nah in this sentence mans in awe. Combine the words, and you get nah jit Trippin
It is when someone is wrong in a way that it makes them sound stupid, as if they are on drugs.
Person 1: Yo man, how do you think that they put ice in bottles but the hole is so small.
Person 2: You are trippin off the perc 30 if you think how that is how it works.