A variant of Herp Derp, Herp da Derp is:
1.) An expression when someone says something obvious.
2.) An expression for when someone says/does something stupid.
3.) A random expression usually used during an awkward silence, but can be used out of complete randomness; can also be used as a greeting.
1.)Guy1: Canada is a country.
Guy2: HERP DA DERP!

2.)Guy1: I just drove off a skyscraper on a scooter.
Guy2: HERP DA DERP!

3a.)Guy1: I'm gay.
Guy2: ........ HERP DA DERP!

3b.)Guy: -opens chat room with random friend- HERP DA DERP!
by herpdaderp:D August 19, 2010
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What one says when there is nothing else to say.
Man-"I cheated on you with your mom"
Woman-"herp de derp"
by LAbabayy April 20, 2011
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a) humping the air.
b) doing the nasty.

Can be used in context of other people/things, like "herping her derp" or "herping its' derp".
a) Guy: Yo, did you see Miley Cyrus herping her derp on that award ceremony last night?
Guy 2: Yeah, looked like she was having a seizure.

b) "Yeah, I was herping my derp last night with that cheap skank, I think I have AIDS now."
by r u srs June 25, 2010
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A phrase originating on South park. It was used to insult Rob Schneider and his various roles. Used to express that there's just no point in explaining how ridiculous his roles are.
by Kaira Pepper April 11, 2011
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