Well it does stink that he is using it to buy other stuff.
However, when you post stuff in the pay it forward thread, paying it forward doesn't mean you hook someone up with something and then give them stipulations on how they can use it. Otherwise, you weren't really paying it forward, you were just trying to help someone AND feel good for doing it. But, generosity is its own reward. You were a good steward of what you had, and you can't be responsible for his actions. Now of course I can understand that you are upset. But, you are only upset because you had expectations. I have sold for dirt cheap or given away lots of stuff here, but I never set expectations of what people will do with it. Don't let this sour experience prevent you from doing what you want - which is to give. Giving is the best - whether it is your time in service, money to the poor or people in need, or a jacket on NS. Keep doing it and forgive and forget.