A sexual partner that just keeps coming back no matter how many times you throw them away.
See also friends with benefits and booty call
Pete: "Last night Haki came over to my room for some pillow talk..."
Pete: "I know! I thought I got rid of her last time when I slept with her best friend!"
Rico: "Looks like you got a boomerbang on your hands."
Pete: "I'm not complaining."