Try watching the film Sweet Sixteen, it is set in Glasgow and I had to put subtitles on just to understand what they were saying.
This is common in Essex "I'll shank you bled! Brap Brap"
I don't even know what Brap even means.
Brap brap is like woop woop! If you want to hear slang that you don't understand, watch Kidulthood, Adulthood or Sugarhouse.