Given that Barty Crouch Sr. was apparently a close colleague of Arthur Weasley, with whom he was on a first-name basis, how could Crouch have mistakenly believed Percy Weasley's last name was Weatherby?
In the Goblet of Fire, Crouch mis-names Percy in the middle of a conversation with Arthur in front of several members of the Weasley family:
“Oh,” said Mr. Crouch, looking over at Percy in mild surprise. “Yes — thank you, Weatherby.”
Fred and George choked into their own cups. Percy, very pink around the ears, busied himself with the kettle.
“Oh and I’ve been wanting a word with you too, Arthur,” said Mr. Crouch, his sharp eyes falling upon Mr. Weasley.
And moments later, during the same conversation, Crouch says:
“Thank you for the tea, Weatherby.”
I gather this is intended as a humorous moment by the author (and it is), but it's hard to accept as remotely realistic.
How could Crouch possibly mistake the son of a close colleague with such distinctive features (red hair and freckles), especially in such an obvious context?