1. Derp: Hey man, what were u doing in the market?
Herp: Nothing man. I was just derping around.
2. Mom: Stop derping around on Facebook and study.
Son: Shut up, woman.
Mom: WHAT DID U SAY??? Herp derp.. blah blah.. blah blah.... No XBox for a week.
The act of being a complete and total fool, jackass, or moron. Doing acts that are not considered proper in public, or even in private. Only the dumbest of people can achieve the level of hardcore derping. A prime example would be when Simon Cowell completely degrades a great singer, that is hardcore derping.
Bob walks in. "Man you were Hardcore Derping it at the party tonight". John throws beer can at Bob. "Derp."