To be honest, I don't see the difference with playing with other people. If the both of you know the 'rocking and rolling' of poker, there should not be a problem, in my opinion. The only time you shouldn't play for money with your friends, other then some cents, is when the other one just started playing poker. But even then, the friend must be smart enough not to do that, right? Putting some money in a game or even throwing it away, stays the responsibility of the one doing it, not? The only thing you can do as a friend, is explaining some dangers.