1) The sound of a Brain-fart, usually when a fairly smart person says something
that's rather silly
by accident or the wrong word or can't think of what to say.
2) Breaking something
or crashing into something
due to thinking too much.
3) Being silly
and not caring
what other people think of you. See dork
"It'd work better if you used contrasting colors. No, not contrasting -- Contrasting. Not contrasting! You should use contrast-gah! Do you know what
I'm trying to say?"
"Derp! YES! THANK YOU!"
"Did you hear the professor walked into a wall today
on his latest thesis?"
"Ha! No I didn't. He's such a derp"