I think the core point that divides creepy/suspicious compliments and genuine ones is your motivation behind them. If you're searching desperately for something nice to say to the girl at the crosswalk because she has great cleavage, it's never going to sound sincere, and she will pick up on it.
However, the exact same compliment delivered out of a motivation simply to put a smile on someone's face can go a lot further. I used to wear quite quirky clothing and getting a compliment on my wardrobe choice would make my day. When I give someone a compliment, that's what I'm trying to achieve - I'm not trying to make myself feel good, or get in their pants, I just want to pass on some of the good will and good feeling that has come my way in life.
However, the exact same compliment delivered out of a motivation simply to put a smile on someone's face can go a lot further. I used to wear quite quirky clothing and getting a compliment on my wardrobe choice would make my day. When I give someone a compliment, that's what I'm trying to achieve - I'm not trying to make myself feel good, or get in their pants, I just want to pass on some of the good will and good feeling that has come my way in life.