When you yourself are stuck between two people that want you (be it sexually, emotionally, for a relationship, or simply due to territorial instinct), and consequently hate each other.
Works for either two women jealous of the other for being around one guy, or vice versa.
Dude: "Oh, man... is that Karen??"
Bro: "Woops... yea... she totally just saw me with Steph!"
Steph: "Who's Karen???"
Dude: "Wow... well, I hope you enjoy your peanut butter and jealousy sandwich."