the guy that wrote "I am a Japanese school teacher" exaggerated like hell, and I suspect made a lot of it up. I've never been kanchoed at school (I almost was outside of school at a party, but I successfully defended myself), and although most of my students are pretty well behaved I have a few that act up. If one tried it I would turn around and yell "Yamero" loud enough to make him pass out. Trust me, that would work; I have made a tough baseball player kid cry once already with that. The gaijin smash guy most likely kinda whined "stop it" and tried to block them... then they think you are playing along and continue to try.
As for gaijin smash, it's not something you "experience" and it's really not something you should use when in my line of work. It gives the impression you don't give a shit about japanese manners and politeness. I've never done it on purpose.
My students say stupid things all the time. It wears off a bit, but sometimes it is still funny. "I need a cell phones. Because it makes me happy." That one was cute, for example, and that was just yesterday.
Jstreet: my students are junior high school, 12-15 years old. Some are very tall. There is a girl in 3rd year here who is over 6 feet, easily.