I would call him out on it the instant it happened, and do it in front of the girl. After he does something ridiculous, turn to her and say, "awww! That's cute. He's showing off - he must like you!" And do it with a legit smile, act like you are encouraging the girl to appreciate the gesture. Then watch as his market value takes a nose-dive.
And that ties in to a larger idea, if your attitude in these situations is always "fine, you can have the b!tch if you want her that much," then the woman will never go with him. It is evolutionary psychology at work. The harder he tries, the less his value must be. That's why he never gets attractive women.