"You're a nice guy but...
- you're not my type."
- you're too old for me."
- you're too young for me."
- you're not rich enough for me."
- your car isn't flashy enough for me."
- your cock's not big enough for me."
- your cock's too big for me." (OK, OK, never heard that one)
- you're too nice." (i.e. "I prefer a guy who treats me like shit.")