Ask him to pay in instalments. If he can`t pay you in one lump sum he`ll probably start avoiding you. At least you`ll find out if he has any intention of giving you it back.
what about taking 'goods in lieu' of the debt?
i.e. what he bought with it.
If you have no proper I.O.U drawn up how will you prove it was not a gift ?, or that the transaction ever occurred?
If you have nothing in writing and no proof that you gave it, then you have not much hope. If they have genuine money difficulties then instalments would be the best idea, but if they are just happy to let you whistle for it then all you can do is cross them off your Christmas card list.