Jump on a grenade

The generous act of flirting or even dating a certain individual to distract them from, and possibly loose interest in a different individual (usually a friend).

Guy 1: hey man, I need to ask you a favor. I think Nicole is hitting on me.

Guy 2: need me to jump on a grenade?
Guy 1: I mean if you could that would be great. I don't wanna date someone who smells like celery, and I don't want to explain why.

Guy 2: I got you man.