Let's face it when a girl says to a guy "you're a nice guy but..." the guy is screwed. Majority of guys I meet are nice. They just have other qualities that outdo that, they have a good sense of humour, intelligent, adventurous, charitable etc. If the only redeemable quality a guy has is the fact that he can be nice in a social setting, then he's most likely bland/boring and not very fun to be around. My two pennies.