I can't get on with on-ears, either.
I've tried a few and after quite a short while my ears start to ache.

The only exception are B&O Form 2, they are as light as a feather and I can wear them for as long as I like without problems. They don't grip much either, which is great for comfort, but they can tend to slide off without due care!
I love the sound of them, too. Amazingly open and detailed with decent if not very deep bass, so not for head-bangers. In fact I prefer the B&O Form 2 to most cans I have tried at any price.