Yeah, that one's been seen to. Bad fish.

It would be applicable in-canon though, no?

I'm still not quite sure what he was planning to do there.

Some forms, yes, but not to the extent it sometimes gets written.

Perhaps it is a British thing. "Weed" is a perfectly good insult in the lines of something feeble and lacking in vitality. To quote Molesworth; 'thou art a weed and a wet and I shall utterly tough you up."