Pretty sure it's from a post Null wrote on Blockland when he was a teenager after his mom's boyfriend burned their house down and killed his cat. Imagine... a teenager who hates his parents. What a novel thing.
I don't know why Ralph is so focused on this in particular, probably projecting his own mommy issues since he refused to drive his mom to her dialysis appointments because he is a junkie loser, which contributed to her premature demise for which he was not present either. Ralph has lived with his mom for 37 years and treated her like absolutely shit the entire time.