I'm going to joke about my friend being poor.
Why make fun of your one friend? Do you have other friends?
No, I've got only one true friend. It's my dog and he can't talk back.
Mocking someone's financial situation is very hurtful behavior. Rather than put down your friend for being worse off than you, try instead to give your friend better support so that he can have the self-confidence to better himself and his financial situation. Your friend will be very appreciative of your help and you will feel good about doing the right thing.
WTF, I just want to make a joke. It's all good, I'm going to laugh at him again later and he won't respond to that.
Do not laugh at your friend, you could hurt their feelings.