It's not even the loud pipes....it's the obvious look for attention with the revving at stoplights. Nobody cares that you ride a bike that millions of others do also, you're not unique or special.
One of my friends who rides HD would give me some line of BS when I asked him why he revved or "blipped" the throttle every time we had to stop. His explanation was that the motor would "load up" if it idled too long and you had to keep revving it to keep from fouling a plug. Of course the BS alarm instantly went off, but then I remembered it is a Hardly cement mixer motor, and realized that it wouldn't be the weirdest thing about them.