Burn that, burn it. Made up while using marijuana, it's often used when one is impatient or when one is talking or telling a story and isn't hitting, or lighting up the joint. It is also used when just sitting around, or after preparing to hit a bong or while hitting it.
Dude, burnat real fast, shit you'll be high.
Man, just burnat it'll burn, but it's going slow as hell.