How do you impress a guy in pe class?

I am assuming this question is directed towards teenagers. Be that as it may, all you have to do is try. Do you think a guy likes watching girls stand around talking to each other? No, just put an effort in, (not too much though. Don't go and get yourself extremely sweaty or anything) Just enough for him to notice you.

NOTE: if your horrible at a sport say soccer or something, stick to defensive positions. If its hockey, play defense. Same goes for pretty much all team sports. That way the attention is not directly on you, but guys will still notice that your active, (and will start to check you out too!)