Flirting is by definition not "blatant." So there's a very thick line in my opinion. Of course, it all depends on perception, but I think it's a high threshold. By that I mean that I only feel a girl is blatantly coming onto me if she is say wrapping her arms around my neck and grinding against my leg, or something of the sort. However, I consider flirting anytime where contact is made, like say, touching a person's arm during a conversation. But then you see that same girl touching some other guy's arm. That's the distinction.

My point: There's not a fine line between flirting and a blatant come-on, the fine line is what differentiates so-called "innocent" flirting and, hehe, "premeditated" flirting. 1st degree flirting: Sentence= sex. Hooray!