One on a motorcycle but only if there is an appropriate seat fitted.
"Most" motorcycles are equipped to accommodate one rider(driver) and one passenger. If you have a side-car then you can have up to three passengers.
No.
Maximum for an airbus 550 passengers.
all were stupid
Here's are the answers given in Timberwoof's Motorcycle FAQ: How do I ride with a passenger? Don�t, until you have enough solo experience. After that, go slower and brake earlier. How much...