Charlie, flirting is inappropriate. Joking is OK, but flirting is not. If you do not understand the difference between joking and flirting, then be on the safe side and don't joke with women.
Cheating, adultery, infidelity, call it what you will, but this is not only actual physical sex, it is very much also in an emotional contact.
Do you flirt without feeling some attraction inside you towards the woman you flirt with? If you do then that is emotional cheating. If you do not feel anything, then why do it? She must still feel something and you are leading her on. That is wrong.
Either way, flirting with other women is not OK for a married man, it is emotional adultery.