Blllll pronounced (Buhl) and spelled correctly with 5 L's, is a common word in upstate New York. Mainly used in the St Lawrence County region it has come to mean "You are stupid" or "Shut up". Sometimes Blllll is associated with a handsign which is most easily described as a horizontal peace sign under the chin with the fingers pointing towards the person.
Many adults and students in the region now know the sign and it has become common for some.
Person 1: Dude I am really awesome at HALO2.
Person 2: Blllll (Buhl). You are a loser.