What Honeycurls said. I'd immediately lose respect for someone who posted pics of strangers on facebook so he/she could make fun of them. IF they're going to do that, they should at least have the decency to blur the face. Can you imagine becoming some sort of bad fashion meme?
I also hate it when my friends post and tag pics of me on facebook. I'm decently photogenic, but sometimes someone will come to one of my band's gig and take pics, then upload them and tag them to the band's fb page. I HATE some of those pics. They always choose the ones where I've got my eyes closed or am making a weird concentration face. Then it's there for everyone who looks at the band page to see. Ugh.
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?