To have ones hat on ones ass. The ass is not the most common area to place ones hat. Hence the implication that to have ones hat on ones ass is just plain stupid. Often used when drunk to refer to someone who has just broken a pinki promise.

a unit vector in the ass direction
(similar to i hat, a unit vector in the i (or x) direction, j hat, k hat, etc.)

plural form of ass hat

one who is oblivious to the world around them,lacking common sense,their head might as well be up their ass.

One who shows so much ignorance to the world around them that it seems as though their head has been shoved into their rear-end, using it as a hat.

The process of shoving your head up an ass, all the way, and wearing it for whatever reason you wish.. to block the sun, or fashion exetera.

Asshat

1. milder form of asshole. comes from old online forums. all swearwords, including any combination of "ass" and "hole" was considered vulgar and would get your message censored and possibly flagged, but "ass" was just fine. so ppl used "ass hat" cuz everyone knew what you were referring to plus you avoided censorship and web filters.

2. ppl now use it to refer to brownnosers or bull-headed douchbag asshole bosses.