Intrusive thoughts of self-doubt and despair, often associated with depression or anxiety, that crawl into your brain and make it hard to focus on other things.
I was going to go to the party, but my brain-weasels were so bad that I couldn't deal with other people that evening.
by e.m.b. October 22, 2015
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A common condition where someone makes repeated grammatical errors, often followed by hysterical laughing and joking. The only cure for brain-weasels is to suffocate them by smothering the victim with a pillow.
Crap, you're infested with the BRAIN-WEASELS! Quick, smother him/her with a pillow.

*followed by a small footchase and a pillow smothering*
by Noah February 2, 2005
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