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1.
when you have a diet high in greasy food, you leave behind residue in your underwear called shartmarks when you fart. your farts have liquid fuel that occasionally, accidentally end up with a bit too much substance behind them.
"too much take out has left Steven no choice to replace his boxers due to excessive shartmarks"
by stevenjchamplin December 26, 2012
 
2.
1. Flecks of poop shrapnel left behind after pooping in a toilet.

2. Marks left behind in your underwear from sharting.
After your daily deucing, check under the seat to make sure you didn't leave any shart marks, especially if you're pooping at a friend's house.
by PooEtiquitteEnthusiast August 23, 2011