That is fine, but posting their picture is so wrong. She took their photo, while smiling at them. And then she captioned it: "Offenders" and put it on twitter.

This is the real issue here.

Let's for example go to your hackathon in Vegas. Lets say some asshole says something inappropriate to one of the high school girls in attendance. Do you really think that taking his photo, captioning it "pervert" and posting it to twitter is the right course of action?