My friend has a problem with playing out of his bankroll

[Awesemo]

One of my friends, who is pretty good at poker, has a huge problem about playing out of his bankroll. He deposited $100 a few days ago and jumped straight into 5/10 shorthanded games on partypoker. Now he's playing 10/20, with a $900 bankroll! I try to tell him that even if he was a perfect player, he has a very high chance of busting out. He says that he knows he is playing outside his bankroll. The problem is that his mommy gives him a $100 a week allowance, and he keeps losing the money. What should I say to him? Is it even my responsibility to try and stop him from losing his money, or should I just bite my tongue?