If you can't work, teach; Can't teach, teach physical education.

This sentence is a classic expression. This sentence is in

In Mission Impossible 3, Tom Cruise met his team members before carrying out the German hostage rescue mission. His old partner was a big black man named ving.

Rhames said this sentence

The "for" here

those

who

cannot

Do,

Teaching means "I can't do it myself, I can teach others to do it with my mouth", which is obviously poking fun at Tom Cruise.