Things I don’t understand…

I see this alot on some of the blogs I frequent;
Ass Hat.
What is an ass hat?
Can some one tell me?
Is it a bonnet worn by a donkey? Is it some sort of outer wear that you place over your backside? Literally a beanie for you bum?
Can someone please explain.

Update on Ivy

Ivy had a hearing test today and passed. That’s the good news.
When the audiologist checked her ears out she found:
Grommet out on the right side and rip roaring otitis media. (Her ear drum perforated on the way home).
Grommet in on the left side but discharging again.
Poor baby.
The paed is missing, presumed dead.