A fork of Rural Dictionary
When one has a flu accompanied by fever and tries to fart. The result is usually liquid poop filled underpants. The term is a combination of fever and shart.
Ryan was sick with a fever for days, and when he thought he was in the clear to let out a fart, he ended up fehrting himself. "I thought I was over that flu, but when I tried to fart, I fehrted all over my self." "I know. I can see the shit running into your socks."