People who think that the louder thier car, truck, or motorcycle is.... the cooler it is.
I'm not a big fan of loud vehicles myself, but as a long time motorcyclist I favor loud pipes on bikes. Some are excessive, but I purposely modified my pipes to make them louder. Not because I thought it was cool, but because it helps other drivers to be aware of a motorcycle in their vicinity. And it worked. After making the change, the amount of drivers unwittingly moving into a space already occupied by me and my bike dropped dramatically.