Whistling. I just can't do it, all I'm able to produce is a pftfhptphpth sound.
Talking about feelins, any kind. I have so many of them that I can't put them into words, and when I try it just doesn't sound right. Pretty darn shitty if you're talking to a psychologist and you have to explain something 3x and it still doesn't feel right.
I suck at all things Neopets. Not even going to go into that.
Communicating on anything else than a chatting app, apparently. I mean I have been here a while but I just suck at making friends on forums.
Suppressing my gag reflex. I'll slightly touch the top of my mouth with my toothbrush and start gagging. Not cute.
I can't sing. At all. My speaking voice is quite pleasant, my singing voice is... Ghastly. Like a cat being maltreated with an iron spike. Yep.
There so many more, but those are generic things like maths, cooking, eye-foot coordination, spatial awareness, etc.