This thread has been dead a little while but, the humor description I kept seeing started to grate.
If I made a joke someone claimed was offensive, that person from that day forward would be considered annoying and though my joking ranges greatly, every joke I'd make within an ear shot of that person would be something I'm quite sure they won't like. Even if that "offensive" joke isn't a common type by me, out of spite towards oversensitive people, I'd make exceptions.
And you're right, you wouldn't find them funny and it wouldn't just be because of the "type" of joke it is. I wouldn't be the person delivering the punchline. It's your reaction that would be the punchline.
I would let it go on until you finally figured it out for yourself. I would also hope, at that time, that you would start avoiding me or not want to talk to me. I can't stand being in the company of whiners. Especially ones who can say they recognize something as a joke yet at the same time can take offense to it. That's like saying "I know that no offense was intended, but I'm going to make drama anyways because I'm a self-righteous tool who feeds off of playing the victim." It's people like that, that cause me to wish for natural selection to make a comeback for the good of humanity itself.