I'm going to make a joke about my friends upcoming hair loss due to chemo
Why would you joke about that?
I thought it would be funny.
That might really hurt their feelings. You need to be more respectful and let them know you are there for them.
I'm joking about it. It's not like he's going to die from his cancer or anything. I know that's not the case.
Even if your friend's cancer is highly treatable, he is still probably very scared and the hair loss will likely be very traumatic for him. Don't you think it would be better if you could come up with jokes that get his mind off of the situation he is in?