There are three ways that I've tried to get people to stop doing stuff. The first is to ask them to stop. That sometimes works; more often than not the other party says "Hey, that bothers OldPrussian. Let's do it more!" And the problem gets worse instead of better.
The second way I've tried to get people to stop doing things is to make it their problem instead of mine. Once people get inconvenienced by their own actions, their behavior stops pretty quickly. However, you may be seen as being petty.
The third way I've managed to get people to stop doing something is to embrace it wholeheartedly. I make it so that they not only see it doesn't bother me; I make it seem that others take part in it as well.
In this case, I'd make him my condom supply person. I'd call him weekly and tell him I need more. I'd thank him for the gift and let him know that they were very useful. (Whether they were or not is irrelevant; I want him to think he's doing a favor and not that he's making a gag gift.) Give them to friends. Sell them online; it really doesn't matter how you dispose of them. The whole point of this approach is to approach it with enthusiasm and make it more fun for you to receive them than for you to get them. I'd even up the ante - if you have mutual friends I'd invite them to play along as well. "Hey Bob, Fred says you give out condoms. Can I stop by and get some?" That generally turns the tables, is fun for both of us, and makes an undesired behavior stop.
