Yes, it could be more like:GM: No Xs in this campaign.
One week later
GM: So what's everyone playing?
Player: I have an X.
I thnk that in this most basic of situations the player is a dick. Assuming there is no miscommunication the player is a dick. There's not really anything more to be said about that. So of course the thread becomes about miscommunication, because that is something that we can talk about.
GM: No Vowels in this campaign, it's Consonants only
One week later
GM: So what's everyone playing?
Player: I have a Y
GM: I said no Vowels!
Player: Y isn't a Vowel
GM: It can be, or at it's least similar to a Vowel, why are you trying to subvert my campaign?
Player: Well, I wanted to play a U but you didn't want Vowels so I thought a Y would be a nice compromise
GM: Actually, we are now using the Welsh alphabet, so Y is definitely a Vowel and you can't play one