'Derp' is a term popularized by South Park. It's sort of a random utterance, such as "blargh". It was used in South Park during a fictional Rob Schneider trailer. Since everything's so generic in his movies, they made fun of them by filling all the description in the trailer with random bits like 'derp' and 'titilly tum'.
By herping and derping.
"Derping" refers to engaging in silly, clumsy, or foolish behavior, often in a lighthearted or humorous way. It can involve making mistakes or acting in a goofy manner, typically without any serious intent. The term is commonly used in internet culture to describe moments of absent-mindedness or playful ineptitude.