I've never heard people say "whom of which," but apparently it's a thing. 

Linguists are studying it, and what's fascinating is that it follows its own grammatical rules. 

h/t nostr:npub18uh265t6krc9c05ytass490q8q6t62glzw9r4squl5n8cky746wss47xlx 

https://news.mit.edu/2023/whom-which-trend-linguistics-0927