So, this just happened to me on campus.
Some middle aged dude (clearly a student, not an instructor) walked past my table in the cafeteria where I was reading news on my phone, alone. He jeered at me and yelled "smile!" and was staring at me in an intensely creepy fashion when I looked up. All I could manage to do was glower and glare, and eventually yelled "no!" once I sort of came to. (He'd walked off a bit by then)
Ugh, I hate this shit. It's like creepy, condescending, ultra slimy covert street harassment. What do you guys typically do in this situation?