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1.
The act of saying something completely inappropriate unintentionally. This is for scenarios where it is greater than mild word vomit and happens with more information that has somehow fallen out of your mouth.
Girl 1: I don't know why Jordan has been acting so weird. It's probably because he loves me and is feeling embarrassed about it.
Girl 2: It's because he slept with me. And he thinks you're crazy. And annoying. And he is scared that you will like, kill him if he says anything. And he's been cheating on you with practically everyone we know, for like 2 years. Oh crap, I didn't mean to tell you any of that. I just had mouth diarrhea.
by PLBB782 July 11, 2008
 
2.
Mouth Diarrhea occurs when you are eating, and someone makes you laugh. You are unable to swallow due to the fact that you are laughing. Food then spills out of your mouth along with any saliva in your mouth. Often the food will be discolored and mushy.
**Two people at restruant
Girl1: And then like, she freaking jumped in front of the car!!

Girl2: OH MY GOD! *laughs uncontrollably*

Girl1: Wow...Nice going. That's some pretty severe mouth diarrhea lol
by Sister Nightroad March 19, 2009