When I've wanted to fuck my gf really hard and be able to hold off I've taken a mouthfull of her hair and really tried to think of nothing but just what was in my mouth. I don't even know if she knew I was doing it; she was off in ecstasy.

Doesn't work all the time, course, but it helps when it's needed. If you thought about it carefully, you might be thinking, how can she not have noticed him munch on her hair? The answer is--when we fuck we usually don't look at each other. She's looking away and my chin's hooked over her shoulder.