No, for several reasons.
1) I live my life by thinking how my actions would make me feel if I were on the receiving end and I know that it would all but break me if my other half cheated on me. So I wouldn't do it.
2) I would refuse, on principle to be the other person. Call it selfish or whatever but I don't want someone who's already taken. If I'm going to bump uglies with someone, there attention better be on me.
3) this person is obviously showing no compunctions with cheating on their partner. Past experience, through myself and my friend's relationships has made me feel "once a cheater, always a cheater". I wouldn't want to get involved with someone like that, even if just for a one night stand. It'd make me feel used. and fuck that.
4)Have you seen me in a social context? You couldn't get someone to have a one night stand with me if your life depended on it. I'm the kind of person ugly people look at and go "Hey, at least I'm not that guy."