I despise my roommates boyfriend
ouch, did he do something to you?
Nothing really, I just think he look like a loser.
Not liking someone is fine but if he hasn't done anything to you I hope you at least show him some respect. Treating people with respect is how you should approach anyone who hasn't wronged you in some way and "looking like a loser" definitely doesn't count.
It's my house too you know.
Even if she has him over you need to treat him with respect. If she has him over too much and he is almost like a 3rd roommate you need to talk with her about him paying rent or finding a new roommate.