...yes the other flirting threads have been my inspiration, but this one has proper questions AND EVERYTHING.
Being a staight male I've only really noticed girls flirting, so I can't offer an opinion on boys doing this.
I think it's fine in most circumstances if the guy is comfortable with it, but sometimes they won't say anything regardless of whether they're fine with it or not. I know a guy who had quite a flirtatious girlfriend and we all thought he was fine with it, but one day (New Years Eve I think) he got upset by her "antics" and broadcasted his insecurities to everyone. This was made harder by the fact he thought she was far too good for him (looks wise). I actually felt guilty for encouraging her on occasion with this kind of flirtatious banter, despite not knowing he felt this way.
It's possible that some people don't always realise they're doing it and these things come naturally to them, but in another example a girl said to me "You only smile when I flirt with you Frank" so she blatantly knew.
In fact there are better examples now I think about it, sometimes from girls I wouldn't expect to be like this... maybe it's just another way of communicating, a sign of affection, it doesn't have to mean anything more.
What are your feelings on this, is it acceptable? Does it completely depend on how your boyfriend/girlfriend feels? How would you feel about it? Are you naturally flirtatious and does it get you into trouble? etc.