When he won't even admit that he has a disorder
My partner is one of the poster child cases. He has never been diagnosed, though, and doesn't believe in ADHD.
When we were getting dressed yesterday, I had to tell him to put on a clean shirt. We had the same conversation the previous morning, but on that day he had already put on the dirty shirt and was too overwhelmed by the concept of changing. So yesterday I caught him in time and he finally abandoned the tee shirt he had been wearing for five days, including two of yardwork. Next!