I think I find it offensive when people say "I hope you’re kidding," because hope is a pretty serious belief/emotion and kidding is by definition a pretty light thing. To hope someone's kidding feels like misdirected energy.

I would say that the solution is to just assume that whomever you're speaking to is kidding because assumption seems generally safer on the surface, but that's probably not the answer either.

Maybe everyone should just shut up.