What is flirting?

All of the above. Flirting is being overly friendly/overly affectionate when the situation doesn't call for it.

However, it's completely subjective due to people having different definitions of flirting. For example, if I were to tell a man he has a nice beard, he'll probably think I'm flirting even though it was just a simple compliment.

It can have intent or just be for fun social interaction. Depends on the ppl involved.

no comment, I thought you said fisting

Flirting is sassy.