"Who is in the toilet?"
I would also start laughing (American English speaker, here). But this is correct. This is from some dialect of British English (I'm not sure which.) You hear it from Moaning Myrtle in the Harry Potter and the Chamber of Secrets movie (talking about when she was alive, so not actually fitting inside the actual toilet bowl!). You also hear this usage in the season 4 Doctor Who episode "The Unicorn and the Wasp". This episode takes place in early 1900s England, and the usage of "toilet" instead of "loo" is used to identify someone as low class.