1) When someone gets excited playing a card game (ie Monopoly Deal) and spills food on themselves.
Dammit, you spilled food again! What a Derp Mah
The art of dropping something you shouldn't have been holding in the first place.
"don't twiddle-derp the punch bowl, Steven, you're quite drunk."
When you take a shit and the outcome looks like Eli Manning.
Dan ate a bunch of Indian food and had a record setting Derp Drop. It was a spitting image of Eli Manning.
when someone is being stupid on purpose, and not caring.
Geez Adam, why are you being such a derp head?
When a collection of people prone to derping gather and try to out derp each other.
Mike Huckabee and Rick Santorum seem to be having an epic DERP OFF.
Kevin is derpping while playing Immortals Fenyx Rising