Can't vouch for any of this but who cares? It's fun.

How do you lock your knees...?

9. If you lock your knees while standing long enough, you will pass out.

That happened to me. I was in a wedding. I passed out during a prayer. Oops. Yes, it was mortifying.

How do you lock your knees...?

With your keister?

In reality, you stand at attention with your knees stationary and as far back as they will go. If you do this for long enough without movement, particularly during a hot day it evidently restricts blood flow and you pass out. I came close during ROTC training but never passed out.

Love fun stuff like this.