Must tense up to orgasm... Anyone else?

For some reason the only way I can orgasm is if I straighten my legs (tense up all the muscles in my legs) and then when I orgasm, I relax. My boyfriend (of almost a year) is used to it and doesn't think it's weird, but I'm worried it will weird future guys out (I'm going to college next year!) Anyone else experience this or anything like it??