Yes, I have witnessed it. It might have been when I was in 6th(?) grade. We were all standing in two lines across from each other. Not sure what we were in line for. Across from me, this one boy was animatedly, happily chatting away to a boy next to him about what he hopes Santa was going to bring him for Christmas. He started going down his list.
A few boys down the line, another boy heard him and started sneering at him. "You still believe in Santa Claus?!? Santa still
brings you stuff? How OLD are you???"
The first boy turned and kind of flinched in emotional preparation of the onslaught he must have recognised was coming, as he turned to the bully. He was a rather chubby, awkward boy. The kind that gets picked on a lot for just being chubby & awkward. He must have recognized the venom that was coming his way.
Luckily a couple other boys came to his defense. One further down the line said, "LEAVE HIM ALONE! SO WHAT IF HE STILL BELIEVES IN SANTA? LEAVE HIM ALONE IF HE DOES."
Another boy said, "Yeah, shut up! Let him believe if he does."
Both of these boys had been raised right to not burst another kid's bubble about Santa.
And the bully, as they do when confronted, shut up.
The first boy, turned forward. But, he was rather subdued after that.
Not only did he not want to put a target on his back again, I think I kind of saw the gears in his head turning. Unfortunately what the boys, who stuck up for him said, was kind of puzzling. "So what if he
still believes in Santa?" As in, "People DON'T???" and "What's wrong with believing in Santa?"