someone has to shit really bad and puts his/her hand over the ass hole. Some shit comes out but is stopped by the hand. It hardens into a brown hat that covers your ass hole.
"I was brown hatting so hard yesterday bro".
when you fart and there happens to be someone's head right by your ass either bending over to tie a shoe, etc, or an unfortunate child walking by....
i was doing the dishes and let one rip just as my son walked by, gave the poor kid a brown hat...
The result when performing anal sex when reciprient needs to evacuate his/her colon.
I was pumping away and when I finished I realised I had a brown hat.