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2.
The slow painful way someone who is following a completely derailed train of logic will support or arrive at the most absurdly stupid conclusions.
Watching her Barbie-doll Brain work it's insidiotic pattern was like rubbernecking at an auto accident.

The insidiotic monologue he delivered made me seek out the sound of fingernails on a chalkboard.

Listening to her insidiotic explanation of how the colors on traffic lights were actually reversed, I realized that some people didn't have to really understand anything as long as they followed the rules.
by Ironheart January 22, 2011
 
1.
Used to describe something or someone that is both insane and idiotic. Created April 2007 in Decatur, IL at the Decatur Herald & Review Newspaper.
It's hard to tell just how insidiotic Rick James was, but "Super Freak" will always be pure genius.
by Adam Flagg June 11, 2007