We all suck at flirting and recognizing it, regardless of gender. Research has shown that women are absolutely awful at it, too. In fact, it looks like they're actually worse than men. Oh, and to make our collective game even worse, it looks like we're also pretty good at seeing flirting cues that aren't there.
"He just adjusted his junk after coming out of the bathroom!"
"I knew it; he totally wants me."
Flirting is a game of conveying interest while avoiding potential embarrassment. Guys may adopt a style that makes their cues a lot less transparent than the ladies' flirting attempts, which is why women find their signals are much more difficult to catch and easier to misjudge as casual interaction. That's not to say that guys can't gloriously f**k up flirting recognition, too; men appear to be more adept at misjudging the motivation behind all that flirting they may or may not perceive. (Hint: They think it's always about sex.)