My general rule is, if you're gonna pass someone, you should be ready to 'make it stick.' By that I don't mean you have to stay in front of them no matter what; but you should be prepared to continue at the pace you used for the pass rather than immediately run out of gas and make him re-pass you.

Sometimes, if the passees take exception to me passing them and try to run me back down, I'll give them what they want. Depending on my mood, I'll either string them along *almost* letting them catch me, or I'll let them reel me in then squirt off the front, and repeat until they give up. "Ooh, I'm running out of gas... FOOLED YA! Oops, now I really am tired... NOT!!! I give up... NO I DON'T!!! and so on. Once in a great while I'll let them catch me, only to discover they can't rest up behind me because there's no draft. That REALLY irks them.