I don't take pics of strangers at all, if I can help it. I have been known to wait and wait and wait for a public place to clear out so that I can snap a pic of just my subject and no one else.

It's not illegal to take pics of strangers in public venues, but, if you're doing it to riducule them in some way, it's a really scummy thing to do.

Why are you friends with these people who do this again?