I'm relatively new in my organisation, in the first couple of months. I was waiting for a lift to go home, as was a man I'd never met. Suddenly, he reached into my bag and rummaged around. At the bottom of my bag was a bag of coffee which he pulled out, in the process pulling out some tampons, a box of sertraline and athletes foot cream that I'd got from Boots on my lunch break. As we got into the lift, he then started throwing the coffee between his hands like you would do if you're teasing a child and kept repeatedly saying quite close to my face "you're not having it back". At this point, I was really uncomfortable and said quite tersely, you shouldn't go in someone's bag. I think he realised he'd crossed a line and quickly gave it me bag. I found it really odd and feel it's worth flagging to my manager just even for a quiet word about conduct but not sure I'm making a big issue. That said, he made me feel really uncomfortable and is allowed to just forgot. Would you flag quietly with your line manager?