Simon Rex -- Braces are a Buzz Kill!!! (VIDEO)

Simon Rex thinks everyone should have thousands of notches on their bedpost, but he's super cautious if the chick has metal in her mouth.

The rapper/actor was leaving Bootsy Bellows Friday night when our photog dropped some sad knowledge about the average number of sexual partners ... and just in the time Simon reacted, several women -- including a really drunk one -- nuzzled up.