What if you're only trying to keep a light-hearted mood and she's all "Don't talk about it like it's a joke"?

Say..."Its no joke, I'm deadly serious", as you fall off your chair laughing?

I believe,if something bothers someone else we can be kind even if we don't agree.

You've fucked up. You will need to fix this. It is pretty infuriating when I am being serious and my husband thinks it is joke time.