How to destroy a shaky relationship?

I moved in with that chick because she apparently really wanted to live with me. (I'm not sure why, it seemed very important to her, to the point of kicking out her previous flatmates.) Now she has a boyfriend who's an asshole. Man, what a douchebag. He doesn't have the slightest bit of respect for her. How do I destroy their relationship?

you don't

>>1
you fuck him

steal some of her shit and put it in his backpack or something

>>3
You fuck the both of them actually.

I actually haven't physically moved in yet. I'm going to see her tonight. What the fuck is going on.

She doesn't want to fuck you, just to make you jealous and to fuck with her botfriends head. Typical woman.

>>7
I can see this be an actual possibility...

>>7
Your logic breaks down where you assume that fucking her is my priority. My priority is beating the shit out of her douchebag boyfriend.

>>9
Sounds like you have your priorities out of whack, then. Because you can fuck her, he finds out, and then you kick his ass. Relationship utterly destroyed; mission accomplished.

I will assume >>9 is OP.
My priority is beating the shit out of her douchebag boyfriend.
Ok, what holds you back?

>>9
Provoke him until he gets violent and bring him down with some nasty trick and proceed to beat the shit out of him.

I met the fucker today. I'm moving in, I swear I'm going in just to cut his throat open from ear to ear when he's sleeping.