Daaaang! Note to self: Never jump on stage during a Tekashi 6ix9ine performance!

Some dude made that awful mistake at 6ix9ine's Moscow concert and the rapper's security detail STOMPED OUT the guy!

But seriously, Tekashi's putting himself in a dangerous position ... obviously this took place on foreign soil, but back here in the US, he's violated his probation twice and faces prison time.

Watch this crazy video!