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'Mental poo' is stuff that people will start talking about that have no relevance to anything, including the current conversation, and usually includes just random stuff that has no bearing on ANYTHING.

Basically, their head is filled with random shit and they're just spilling.
We were talking about cars and then Jim came over and started spewing all this mental poo.

He started talking about a shit he took and how it reminded him of banging this chick in college and that he needs to go buy bread on the way home.
by moooooog35 October 30, 2009

Words related to mental poo

foot in mouth speaking stupid thinking thoughts