I'll get the ball rolling a man puts £1 into a vending machine for a can of coke but the coke is sold out and he doesn't want another can so he ejects the money and gets 2 x 50p's (i.e £1) he comes up to reception.
Man: I'm sorry I put a pound in the machine and got 50p's back
Reception: Ok sir
Man: Well this isn't my money I put a pound in
Rec: Yes Sir but that is equal to a pound
Man: Yes but this is not my money
Rec: Oh ok sir (realising this is not going anywhere) opens the vending machine and gives him a pound.
Man: Yes thank you this is my pound (it was juat a random pound) I'll leave these with you (50p) in case some one comes back for them

Man: I'm sorry I put a pound in the machine and got 50p's back
Reception: Ok sir
Man: Well this isn't my money I put a pound in
Rec: Yes Sir but that is equal to a pound
Man: Yes but this is not my money
Rec: Oh ok sir (realising this is not going anywhere) opens the vending machine and gives him a pound.
Man: Yes thank you this is my pound (it was juat a random pound) I'll leave these with you (50p) in case some one comes back for them
