The OED. (Try fitting *that* in a tiny browser window...).

One of a teacher's most important responsibilities is to establish a rapport with her students--you can't do that by talking like a priggish Professor Higgins for an hour and a half. English studies--in particular, composition and academic argumentation--has less to do with proper grammar than it does with clear reasoning in language. You can use a Dundee dialect to defend a claim about Shakespeare's chauvinism as easily as with a "proper" BBC dialect.

What you're neglecting to recognize here is the fact that one's *audience* is a crucial part of the rhetoric of any given situation. For example, if, whilst teaching my intro Rhet/Comp classes, I actually used the word "whilst" in the classroom, regardless of whether or not I used it correctly, I would be guilty of neglecting my audience's values and thereby lose some of my students' respect. And if I lose their respect, I lose the ability to teach them important stuffs--stuffs like "knowing your audience is crucial to effective argumentation, in the academy and everywhere else."

It might grate on your nerves, Brus, but then you might not be a member of the audience this teacher is trying to reach. It may be that he's knowingly breaking the rules of normative, "proper" grammar in the classroom because he's trying to establish a linguistic connection with his audience in order to teach them more important things about writing than verb tenses.

W.C. (water closet), porcelain throne, shitter/crapper, john...

Of course, there's also the distinction between the facility and the actual toilet itself...

And, in the U.S., "the loo" would be considered considerably less refined and ladylike.