Mate, sorry but believe me, if you were in my boat you wouldn't dream of saying anything like that, in jest or not. It's just not funny for me at all. At the end of the day a mental illness is going to finish my dad, he falls into the catergory that you're taking the piss out of and it's hard enough dealing with it everyday and then have one of my mates making fun of it for a cheap joke. An apology would suffice but instead you're telling me not to be over sensitive about it.
Sorry but it hurts man.