Algebra
I’m good with geometry, arithmetic, and personal finance — but algebra (and trigonometry, and calculus) confounds me.
Foreign Language
I can follow along in Italian and I know snippets of Spanish and French — but I am utterly hopeless when it comes to actually learning a foreign language. Even my ability to pronounce the words properly is awful.
Sports! My level of athletic activity is going for brisk power walks a couple times a week. When a football game is on TV, it might as well be static to me.
Microsoft Office (I hate it, love Word Perfect Office), Apple products, art history, the art of social conversation, driving and,similar to @SQUEEKY2, understanding conservatives.
A lot of things, but I’ll just say baking and cars. I like to cook, but I’m not a fan of sweets and thus I rarely bake. As for cars, I’m just not interested in cars in general.