Who?

The Man just told me that when he was at school he learned that in proper English you couldn't use the relative pronoun who with a plural subject. In other words, it is ungrammatical to say, for example, People who wear too much perfume should be forced through a sheep dip before getting on the rush hour train.

I told him I'd never heard such nonsense, and asked him what he was told to use instead. He couldn't remember. He thought it might have been which.

"People which wear ...?" I said. "I don't think so!"

"OK, so maybe it wasn't which," he replied, but couldn't come up with a feasible alternative. It wasn't that. He remembered that much.

He wondered whether it was an old rule, since many of the English grammar rules taught at Japanese schools back in the Dark Ages, when he was at school, were already at least 100 years out of date even then. (These days they're 140 years out of date.)

I don't think so, though. Have you ever heard of this one? Which ancient grammar rule could his teacher have been invoking when he got this one wrong?

Incidentally, besides having to memorise a lot of arcane, useless, and frequently wrong grammatical rules, The Man's English education also included various disconnected bits of literature, most of which were meaningless to him at the time. Imperfectly remembered snippets stuck, though, so that I cannot start a sentence, "I wonder ..." without him feeling compelled to interrupt, "Lonely as a cloud." These days I do it too, and annoy my friends.