when i was in high school i had a passing period that i had to go through the library which kind of made for a pinch point. Anyway, there was this guy who i had literally never met or spoken a single word to, and he was going the other direction during passing period and he would come up and shoulder check me. The first couple times he won b/c i wasn't expecting it and didn't realize i needed to brace for impact. After the 2nd time i realized he was doing it on purpose so I would just check him back. (He was also like 3 inches taller than me and probably had at least 20 lbs on me so, ya know, physics).
I actually saw him at a party a couple years after graduation and at this point i'd still never spoken to him, but we were standing in the same conversation circle. So I asked him why he decided to shoulder check me during passing period every day. he was like, "i don't even remember doing that...but, it does sound like something i would do."