In one episode of the TV show Sherlock, Sherlock Holmes is described as much of a grammar guy and love correcting grammatical issues. In that setting, he says this to Watson
Holmes: Oh, you meant "spectacularly ignorant" in a nice way! Look, it doesn't matter to me who's Prime Minister...
Watson: I know...
Holmes: ..or who's sleeping with who...
Grammatically, should he have used "whom"? Because it's the preposition object.