It is when you shart yourself but, only....only when a sneeze is the catalyst.

When you shart and snarl at the same time, usually facilitated by a obtuse sphincter.

How to avoid Schnarting:
-Becareful when you sneeze
-Becarful when you get mad
-Becarful when you sneeze and get mad
-Becareful when you snarl
-Becareful when you need to poop

The act of sneezing and sharting at the same time (i.e. sneezing + farting + shitting your pants).

The art of shitting farting and nutting at the same time

Sneezing so hard that you shit yourself from farting.

A noise you make to denote amusement, preceding a huge outburst of laughter. Usually made by a violent intake of air through the nose and mouth that makes a reverberating snorting noise.