I'm thinking of scamming my friends everytime they ask me to request an uber for them
Why do you want to scam your friends?
I want to save money.
It is not right to scam your friends. If you cannot pay for an uber, then tell them you can't. If you scam your friends, you may lose them.
I know they don't expect me to scam them, so it's a great joke to pull on them.
They will not feel it is a joke if you scam them. It will feel malicious and they may not like you anymore.