Flirting like every other human activity is governed by unwritten laws of etiquette. These rules determine where, when, with whom and how we chose to flirt. We generally obey these unofficial laws instinctively, without being conscious of doing so and only become aware of these rules when someone breaks the etiquette. For example flirting with the widow at her husbands funeral would be: with the wrong person, at an inappropriate time and place.
So be sure to flirt responsibly and if you are lucky enough to be flirted with and are interested then let that person know. - Susan