If my child got a gift that I didn't approve of, I would involve my child in the right decision. I would ask him why I didn't think if was appropriate, I mean to give me reasons why, and make him decide (for himself) why it was not appropriate. In that way 1) Not only would I be making the decsion, but 2) he would be making the decision as well by understanding why it wasn't appropriate, thereby giving him the power of decision as well.
I would have my daughter say for whatever it is, and afterwards depending on what the gift was, i would return and exchange it for something else, give it to someone else, throw it away or save it for a future date to use. If i could not do any of these options for any given reason i would confront the person that gave it to me and let them know what the reason it was behind it and ask them to give them something else or take the gift back dependign on the situation and who it was from.