When I play with my friend, he will often knock his own king over when he is going to lose.
He ends the game and says, "I lose".
Is this permissible?
here is a link addressing this question exactly i quote:
It depends on the way you do it, generally it's not rude, though.
Once I was playing a tough game against the late GM Wojo, and got a balanced and complicated position, but also considerable time pressure. After the time pressure was over I realized that I have totally blown up my position, played 41.Kg1-g0 and pressed the clock. Wojo was surprised at first, but later he had a good laugh.