Flirting isn't that hard with guys, I done it on a few times in my life (only because I want to see how he would reacted; it wasn't like deep flirting but subconscious flirting; so he would be attracted without being aware). That makes no sense, but here is what I did if I can remember it.
If I wanted to flirt I would act more sexual, and giving hints at it. Psychology proves that if you put an association with yourself then the person will associate it with that. So if I smile at a guy while he is talking he is happier because I smile. If he said something funny I laugh more than I would, even if the joke wasn't funny. I cannot go too far with this since the guy is probably straight. If he is talking about a hot girl, then I would get involve in the conversation (association), and describe a hot girl and keep on talking about it. Giving more hints and arousing him by talking about hot girls. I usually can find the number one topic in a guy, he could be smart, dumb, classy, average, jock, anything and I can make up conversation with him.
The last time I did this I think he was more of 'awe' like admiration to a star, I am not sure that's the right word though. But I know for sure he wasn't thinking I was gay, and stuff, since I act straight and look straight. So it's all in the subconscious.
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Girls 'dumb themselves' down because they want the man to feel more dominant and stronger (so he in turn likes to protect the girl). I do that subconsciously as well, but not extremely. More like an airhead feeling, like "Wow that's awesome! That's great. How do you do that. How can you be so smart?". That's not even to guys but to everyone in general.