any person who uses someone else's pre-existing attraction to them to mess up any relationship that other person might become involved in, regardless of whether or not they return feelings of attraction.
Liz could have cared less about Dre's attraction to her when he was single, but now that he's with Carrie, she's acting like a big ol' monkeywrench.
The process by which a female bends a male's penis backwards between his legs and proceeds to suck him off.
In 2001, Mike Krzyzewski, head coach of the Duke University men's basketball team, reportedly gave each potential recruit a monkeywrench upon their official visit to campus. Being eventual Duke basketball players, they all enjoyed this very much.