Acceptable flirting depends on your intentions, and also on how the other person feels about it.
People usually flirt to explore what a romantic relationship with the person might be like, to boost their self-esteems, or help them to get something they want.
Flirting may be verbal, in the form of compliments, bantering and teasing, or it can be a smile, a steady gaze, a toss of the hair or a hand on the arm.
And, of course, it can also be an email or a text, with all those smiley, winky faces.
** By the way, scientists say flirting developed to further the human race, by helping males to find a mate and females to evaluate a potential partner and his commitment before moving forward.