Especially if it contradicts Logic and Reason.
The stupider the better for Knobs.
Me: You are a Knob. There is no such thing as Mermaids.
Sheela: I am going to report you to Yahoo Answers because you made me a sad Knob-Ho.
2. Also can be used as a term similar to goof, tool or moron.
2.Dude, did you hear Bill locked the keys in his car again - what a knob!