it's great to be nice, friendly, have that sparkle etc. However i think it crosses the line if it actually gets to the point where the other person really believes that you are into them and they could "have you" if they wanted. For example, my husband can be nice and sweet, but the only time it would hurt me would be if i thought the woman he was nice to actually thought he was really into her and wanted her..then i would feel like he disrespected me and let her disrespect me also. It would make me feel like, if she knew he was married, that she thought he was more into her than his wife. A man is more attractive to me when he shows loyalty and strength to the one he is with. A quick ego fix is all too easy. A woman i know is the most beautiful person, inside and out, she always has a big smile and laugh, is warm to everyone, and men LOVE her. But she can do all this and never ever ever make you think that she is flirting, she's just cool, fun, happy and beautiful. I think it's great to be like that because she never makes anyone think she has a "romantic" interest. So i think you can be both, have that "flirty" kind of personality but as long as it isn't misinterpreted then it doesn't do any harm.
gee...look at me writing an essay!!! haha