I'm Up

Equivalent to the phrase "I'm up for it," but abbreviated. It's similar to saying "I'm down." Meaning you're interested in joining in on the activity suggested in conversation.

Ron: I'm really in the mood to get ice cream.
Fred: I'm up.

CSB

Cool story, bro. When someone tells you a boring story that really needn't be shared. Sarcastically replied.

Fred: "Yesterday I got a cut, so I put a band-aid on it."
Nick: "CSB."

KFP

Kosher for Passover
Able to be consumed by Jews during Passover

"Can I eat this bread if I'm Jewish?"
"No way, man, it's not KFP since it has yeast in it."