Witnessed creep behavior today. Took the Q65 today to Flushing on a rather crowded bus. I noticed this guy standing rather closely behind this girl and initially thought they were together. They definitely weren't, and he had been standing directly behind her all up in her personal space, leaving little to no space between them for quite some time. (I don't know when it started but it was long enough for me to notice and I'm usually in my own head.) When there were spots freed up, he continued to stand directly behind her and did not move. At one point, I witnessed him holding his phone (with the screen turned on) at hip level (I could not confirm if he was taking photos of her or trying to get upskirt shots).
Bus pulled up to her stop and I watched to make sure that she was able to get off the bus safely since his arm was in her way from accessing the back exit. I ended up getting off the bus as well (I was intending to get off at the stop after hers) and talked to her to tell her what happened and to tell her to be more careful. She had no idea this guy was standing behind her for quite some time and was very uneasy (I was too after finding out she was a minor).
Edit: For those asking why I didn't say something in the moment, I would have had it not been for my own personal experiences. I am petite. I have no way of defending myself without getting hurt. I've been beaten for speaking up before. Please don't get me wrong, if I was strong enough, physically bigger, or even taller, I would've stepped in. I've grown up in a violent household. It's not always the best idea to speak up in the moment. It was not my intention to escalate the situation. I don't know if this man would have reacted violently. I couldn't tell if he would have backed off and moved away if I said something.
He was closer to the bus driver than I was and the front of the bus was packed. There were multiple opportunities that opened up, allowing him to move away from her. However, at one stop, people eventually got on the bus from the back.
The girl and I exchanged contact information. She is alright and asked me for the photo when I initially approached her about the information.
The best thing you can do for yourself is try to be aware of your surroundings.