Ha! My mother was/is also a lot like Joan–the narcissism, the furious tantrums that would go on for hours, the destruction of property, and occasionally the physical violence, though my brother got that more than I did–and I also usually laugh when watching, and have occasionally done dramatic readings of some of the lines from the film. (My favorite: "TINA! [dramatic pause] Bring me the AXE!")
My brother and I both laugh about it, even while acknowledging that it shouldn't be funny for us. Defense mechanism, maybe?
(Bro and I also occasionally laugh when we cringe at some of Tina's responses in the film, like, "OMG, don't say THAT, you're only going to make it worse! Tina, SHUT UP! Just keep your head down and maybe she'll let it go! You'll never win this, just hope it blows over!")