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A slang term for Down's Syndrome.
What's wrong with that guy?

Oh, him? He has the Derps.
by The Gnargoyle October 25, 2010
A symptom found in gamers that causes them to exhibit - often times retarded - and pointless ignorance or devoid awareness of anything that regards intelligent thinking.
Primer has a serious case of the derps.

Or simply imagine somebody being as close to legally considered mentally handicapped without actually being quite there.
by Str8 Derpin' April 04, 2011