Onomatopoeia for the sound created by slam metal vocalists. Presumably, the vocalist making the sound is enunciating lyrics, but they are almost never legible, even if you're reading official lyrics published by the band.
The sound is sometimes achieved through the use of pitch shifting technology.
"Hmm, so Propitious Vegetation's lyrics are about veganism, eh? Well, who knows if that's true, all I can understand is bree bree bree..."
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.