Means to Fart In Self. When you're in a situation, like with a new boytoy (or fish) and you have to fart so bad that it goes up into your stomach making a loud rumbling, grumbling, farting sound. To which you say "hmmm I must be hungry" in a sad attempt to cover up.
Claire - Oh man, I was at Rusty's this morning, and my gas was so bad that I was Fissing like crazy!
Ann - Dude you should have just broken the ice and dutch ovened him
The annoying friend in the group that will do anything to make sure everyone likes them. Usually supplies the rest of the group with cigarettes/booze and tells really corney jokes. No one REALLY likes this person, but everyone tollerates them because they are such a pathetic kiss ass.
Jamie - "Let's get shitfaced tonight"
Jill - "Right on, I'll call Jo over to buy everything"