Guys, When is it inappropriate or cross lines?

OK so there's a guy that I see all the time at my new gym, he eyes me up a lot..(which I don't mind because he's quite attractive) i mean if he's on his phone & spots me, his phone even gets put away (which made me laugh) so minus all the hip/thigh glances, he gives a lot of good eye contact & smiles (I then smile back) again all well & fine. Then.. today one of the workers I know at the gym tole me he's married! Yikes.. I was a bit annoyed really. When is a line been crossed when your off the market.. I get glancing here or there, but all the smiling, checking out & going out your way just to make that eye contact with someone you know nothing can really happen with.. I mean what is the point lol?

Guys, When is it inappropriate or cross lines?
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