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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