Apparently I am constantly flirting. I keep getting in trouble for it.
The vast majority of the time (like, 99.9%) I mean absolutely nothing by it at all. It's just a nice way of giving people an ego boost, having a bit of fun etc. I'm not talking actually rubbing against people, I'm not even sure what it is I do really - making eye contact mostly I think, I dunno.
I get told I flirt when I dance too (I do partner dancing) but that just is because it feels weird NOT to look at someone who has their arm round my waist, and if I keep eye contact and smile I am much less likely to get dizzy and/or lose my lead somehow.
I probably do talk about sex a lot. OK I definitely do. But that's not in a flirty way, I just have a dirty sense of humour, and a lot of my friends are the same.
If people don't flirt back I stop, but I would say about 50% of people do flirt back (it's hard to say cos I don't really do it consciously) Every now and again I get in an outrageous flirt off when I find someone else who is as bad as I am 
I'm bisexual, but I also do move in circles where maybe a third of my good platonic friends are men, so gender isn't really that big a deal (except that men are more likely to flirt back I suppose)
I'm not wafting about in miniskirts and high heels. I basically dress like a slightly vintagey student, I have very little poise and elegance. I am well fit
but I genuinely think that most people are, if they would only believe it.
If I actually fancy someone I usually lose the ability to talk to them even normally and generally act all embarrassed and shy.
That doesn't help though. People keep telling me I was flirting, or telling me off for it. Not the people I'm flirting with though, because I just interact with the person I'm interacting with, not the entire room. And if it is a partner of the flirtee objecting, well they should be objecting to their partner, not to me. I wouldn't have any issue with a partner of mine flirting because, well, it's flirting.
SIGH.
So yeah, does anyone else flirt? And is a bit of harmless flirting really THAT bad?