1) To open and unpackage something, generally for the first time.
2) To operate a motor vehicle in a spirited fashion.
3) To commence, or return, fire at a person or thing.
1) Hey, let's go open up that new PS3.
2) Yeah, just a few minutes ago, we had 'em opened up out there on Redwood.
3) Why don't we take the 1911 out and open up on some bottles and cans?
when a girl opens her legs exposing her pussy
Yo last night I told her to open up and I tore dat pussy up!
To open up, as in to stab/knife someone.
The opening process can be as simple as a minor poke but generally involves heavy bleeding and multiple openings. The more insane openings consist of using your bear hands/fingers to perform the opening process.
"I finna open you up like a damn can-o-tuna, you fat slut ass biotch."