I didn't bother telling the guy who gave it to me because I realized that he wouldn't change his lifestyle, and because he was an evil person who I didn't want to speak to again. Not evil because he gave it to me, but because of other reasons...
I did tell an old friend I had had sex with afterward. He wasn't pleased, but then chuckled and said, "well, I guess I can't say you never gave me anything." You have to decide for yourself.