That reminds me of a really cerebral joke I came up with years ago that almost no one gets ...
English Major 1: "I really hate quantitative article/noun disagreement."
English Major 2: "Amen!"
And not quite as obscure, but still not many people get ...
"Having two flags is a double standard."
And finally, some number humor ...
"She's only 20? Score!"
"12 cans of soda in a case at 12 oz each makes 144 ounces. That's gross."
Person 1: "Do you know what's odd?"
Person 2: "All prime numbers. Well ... even two."