I think sense of humor has been mentioned in similar threads, but here's how it relates to the "not so obvious" part of it.

Notice what categories of things they think are funny. For instance, does their idea of joking usually involve making fun of somebody, or putting another person down?

I can't remember details but my ex and I once read a magazine article together. Subject was how you can't always go by how you feel. Author and his wife had both been down with a bug but she continued to feel awful while he just had a nagging leftover cough. He took her to the doctor. While there, the doctor heard him cough and insisted on examining him too. Well, it turned out she had a bad cold, but he had pneumonia. Husband who felt fine was put on bed rest, and wife who felt terrible was instructed to bring him his meals in bed.

And didn't ex think that was just SO funny.

Remember the book Clan of the Cave Bear? In that Neanderthal society, a woman had to kneel at a man's feet and get his permission to speak to him. Until he acknowledged her by tapping her shoulder, she wasn't allowed a word.

And didn't ex think that was just SO funny.

Maybe it should have been more obvious. He was making it clear what he thought of women and their roles in relation to men. But of course, if I'd listened to my gut instinct, there would have been that "Oh, lighten up. It's only a joke."