1 Suppose that I and my friend are outside of a bus: - If I want have my friend get on the bus, can I say "Get on John!"? Yes, this is correct. 2 Suppose that I am the driver and my friend are outside of a bus: - If I want have my friend get on the bus, can I say "Get on John!"? Yes, this is correct 3 Suppose that I am outside of a bus and my friend is on the bus (the bus has stopped): - If I want have my friend get off the bus, can I say "Get off John! / "Hop off John! / Jump off John!"? Yes, this is correct. 4 Suppose that I am the driver and my friend are outside of a bus (the bus has stopped): - If I want have my friend get off the bus, can I say "Get off John! / "Hop off John! / Jump off John!"? ??? This doesn't make sense. You say your friend is outside the bus so you can't say 'Get off' as he is already off the bus.