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1.
The term Mcshittle refers to the meaning of eating a Mc Donalds breakfest sandwich such as a Mcgriddle or any other sanwich and after 5 mins of being done with it. You start shitting horribly. Thus having the Mcshittles.
I ate a mcgriddle today and 5 minutes later I had to Mcshittle.

I just Mcshittle'd in my pants!!
by johnson l October 17, 2006
 
2.
Gastronomical distress caused by fast food.
Man, after that late nite Taco Bell burrito run, I had a nasty case of the McShittles this morning!
by Mark Trial December 27, 2007