It depends sometimes I say no but the decide to go for it anyway as they start to pass. Normally though I'd tell them "your on" and try my best. If I get beat oh, well. If I win cool! Its all about the workout I would get for the few minuets. Besides unless he is unusally slow for a guy or on 30 pound bike its not a slam to get beat by a guy, especailly if he is on a really nice bike.