The dumbest random pipe in my pile is for a Garelli NOI engine. It’s just the head tube connected to a trashed cylinder, probably why the cylinder got trashed since the rest is gone. I sold or gave away everything that went with that bike but that somehow stayed around.
As far as keeping neighbors happy... On one of the scooter forums a guy built a proper expansion chamber pipe for his bike and then built a muffler around it. The stinger tube does a 180 like most scooter pipes but then the entire thing is inside a larger tube with baffles and everything. Looks vaguely like a stock cheap Chinese pipe and cuts lots of the noise down without being too restrictive due to the size, plus it’s muffling the noise that comes from the chamber itself resonating. I’ve thought on doing something similar on one of my daily riders but always have more important things to do than quiet the bike.