A sound made when you have nothing better to say. A filler during a silent break in conversation. A random sound. Potato.
Ex.
Me: *calls friend on Skype*
Friend: *picks up Skype call* "brrrpt!"
Me: "brrrpt!"
Ex.
Dude #1: "What should we do now?"
Dude #2: "We could brrrrrrrrpt..."