coin personality

A person who is like a coin. 50/50. 50% of the time they're really cool and enjoyable to be around, 50% of the time they're the most insufferable human being ever to walk the planet.

Bob: Hey guys, I brought a pizza and gifts for everyone!
Everyone: Woo hoo!
--The Next Day--
Jim: Hey Bob, what's up dude?
Bob: My foot will be up your ass in 10 seconds if you don't get out of my sight right now.
Jim: Talk about a coin personality...