Self control...over rated

Sometimes I hate having to have self control. My sister is over for dinner, which I can hardly tolerate her. But. It's not only her but her moron of a boyfriend is over too. I'm currently listening to them talk to my grandma (who is gullible) and I just wanna go over and kick him in the nuts. That's how much he annoys me. I can't really explain why or how, but he is just so stupid! Maybe he just annoys me so much because I have a very strong dislike for the guy, but yet I don't think thats it. Sure maybe it increases it, but I think the guy is still a complete moron. Then again so is my sister. Yet I sit here and be nice and polite. Self control is so over rated... HELP ME!