I think we could put "How to Fly Using Your Mental Powers" on this list and it would be more likely than men learning how to flirt without being creepy. This has always been a big problem, but it's come into the spotlight with the #METOO movement. A lot of incel guys will complain that they're not attractive enough to flirt. That girls just disregard them. I highly doubt that. I've seen some hideous looking guys flirt successfully with model-type chicks just because of confidence, being kind, and taking a shower.
You're not doing yourself any favors if you don't try to be a better flirt. One-sided flirting is just harassment. Here's an easy tip. If it doesn't seem like the girl is into it, just say "thank you for the conversation" and walk away. Think about what might have gone wrong, even though it might have been nothing. Just because you flirt with a girl doesn't mean she owes you anything. Not even friendship.