All I can say is that hearing the words "You're such a nice guy" makes nice guys tremble with fear. I've had it used twice as excuses for women acting badly. One actually had the nerve to say "You are way too nice. It's so easy to abuse you. I can't help myself." And then asked where we were going for dinner on Saturday. I'll spare you the response she got, but it was not quite as nice as she was used to.
I would have no hesitation to tell someone he is a nice guy and sincerely mean it as a compliment.. Why am I STILL HERE??