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1.
An idiot to the infinite power. Someone so stupid that even being in their presence can make you stupider. Worst part about a brain slug is that they don't know how stupid they are/sound. They may often use large words to appear smart

Warning....If you are in the presence of a Brain Slug don't engage them in an argument, and/or a conversation JUST LET IT GO.
Reggie: For 20 pts what is 10x1?

Brain Slug: Well seeing as they can be reciprocals of one another I'm going to change the problem into what is 9x2 which the answer is 18

Reggie: What you've just said is one of the most insanely idiotic things I've ever heard. At no point in your rambling, incoherent response was there anything that could even be considered a rational thought. Everyone in this room is now dumber for having listened to it. I award you no points, and may God have mercy on your soul.
by Mayor McCheesenstein June 28, 2013
3 0
 
2.
When you pick a booger and a long string of snot is connected to it that goes all the way up into your sinuses. When you pull it out, you can feel it slither through your skull.
I had a brain slug, the other day. It was impressive.
by King Booger November 21, 2011
4 2