The only concession to safety that a motorcycle needs. Time was, you were expected to wear visible clothing and a helmet and drive predictably. Now it's OK to dress completely in black (no helmet) and pop in and out of lanes at will. As long as you have really loud, low pitched, non-directional exhaust noise.
Loud pipes endanger lives.
"Boy, these loud pipes rock. Everybody takes their eyes off the road to figure out where the hell the racket is coming from and get into massive pileups. Then I just drive around the mess."