In the following, the informer tried to tell a grammatical Knock Knock joke:

I = Informer, M = me (interviewer)

The 1st Attempt:

I: Um, knock knock?

M: Who’s there?

I: Whom is there

M: No…

I: Wait no that’s not right!

The 2nd Attempt:

I: Wait, knock knock, sorry, okay got it, knock knock?

M: Who’s there?

I: Wait, no…

The 3rd Attempt:

I: Oh! Knock knock, got it! It’s knock knock, who’s there, they say a name and then they say “that name who” and they say that name…. Maybe? It’s a grammatical, oh it’s slipping my mind right now, wait! knock knock?

Me: Who’s there?

I: To

M: To who?… too whom! Ah I get it!… That took a lot of trial and error

I: Yeah it did

While, at least by the third attempt, the joke is essentially self-explanatory, attempting to  trick the person who answers second into using a nominative case interrogative pronoun (who) rather than the grammatically correct accusative case (whom), perhaps the amount of difficulty it took to tell the joke accurately suggests a limited usage of technically precise grammar in every day life.