A reply of disagreeance or to insult. One person may be saying or doing something they believe to be comical or impressive. If the person they are doing this in front of disagrees, they will say "buzz". The volume or tone of voice determines how much the person disagrees. It may also be accompanied by shaking the head left to right.
A: Lets go to the park.
B: Buzz. Terrible idea.
A: Oh my god, this shit is so hilarious (laughing)
B: (silence and long pause).... Buzz (while shaking head left to right). No.
A: (watching TV) Oh my god Buzzzz!! This team sucks so bad. We are done. Buzz buzz buzz.