Kendall channels her inner Bruce Lee as she karate kicks an empty glass bottle off the top of a friend's head ... talk about flexibility!!!

The ninja move went down Thursday night on the beaches of Los Angeles ... and you have to give dude props for standing tall and letting Kendall take a crack at his head.

Kendall gets mobbed by her pals after pulling off the daring move ... 'cause it's all fun and games when no one gets kicked in the face!!!

Looks like Kendall might have a future in kung fu movies.