Favourite one, had it happen a couple of times actually...
All day charter in a C210, flying pax around to various aboriginal communities for meetings etc etc. Pull up outside hangar at end of the day, unloading their bags, doing the friendly chit chat, when one of the punters asks;
"Is this a twin engine aircraft?"
"No", I reply, "it only has one engine mounted on the front there"
"Oh" long pause..."so is that a twin engine then?" - pointing to the Navajo parked in the hangar.
"Yes, very good".
TL