"Hurr durr" is the sound of laughter coming from someone with half a brain.
Mostly it is used to point out when someone has made an idiotic claim, though, surprisingly, idiot males will attempt to make thier laugh as deep as possible to make them sound more manly, when all it really does is make them sound like idiots.

A portmanteau of carpe diem, a Latin phrase that means “Seize the Day!” and DM, which stands for Direct Messages. This word means seizing the day via DMs.

the signal that someone has done something stupid and knew such, pissed someone off by doing it, and is used to intimidate the other pissed guy

An onomatopoeia for thunder in some New Guinean language

Coming from the word "harder" , it is the sound that women in pleasure make when they want to more. When you hear this, it is a sign that they are in genuine pleasure, otherwise you will just hear "harder" (when they are faking it).

Hurr durr is a dutch battle call. It comes from 'harder' and means 'faster'.

In the english language, hurr durr can be defined as "HI THERE!"

However, in idiotic terms, we say "HURR DURR!"

It is often said to describe idiocy, or silliness.