PDA in hallways

I just remembered something that occurred during my two week practicum at Oak Bay, and I remember I had no idea what to do about it. There was one senior student, a male, who was in a class I observed a few times, so he knew who I was. However, every time I passed him in the hallway when he was with his girlfriend, he would make eye contact with me, then drop his hand onto his girlfriend's butt and start caressing her butt or squeezing it or something along those lines, then he would look back at me again. This honestly happened like 5 times in the hallways- I feel like the student was definitely egging me on to see what I would do, if anything. Is this even an issue, or should I ignore it? Side note- the butt caressing was definitely excessive, not just a little love pat- seemed inappropriate for a school setting.