Said to someone who is being impulsively stupid or annoying, to try to get rid of them. Can also be said slowly and enunciatively while slowly backing away. Another way of saying it would be to say "Sal are you!"
Can also be pronounced "busul" or "sal", which is basically the natural pronunciation of saying "bye vesal" very quickly.
Guy #1: "Hey man, what's up, how you doin' man? Hey did you see my new bike? It's awsome isn't it? Got it for two thousand dollars!"
Guy #2: **stares blankly at Guy #1, then holds both hands in front of his body, palms facing down, fingers spread wide, tilts head slightly to the right, and starts to slowly walk away from Guy #1 backwards and says slowly and clearly: "bye vesal" or "what a bye vesal are you!" or just any combination of these terms.