"Arthur, old man, what a day, eh? What a day! Could we have asked for more perfect weather? A cloudless night coming ... and hardly a hiccough in the arrangements.... Not much for me to do!"
-- Ludo Bagman, totally missing the feverishly busy Ministry wizards all around (GF7)
First Ludo Bagman, and then Barty Crouch, come by the campfire at the Weasley’s campsite and talk about the pressures and problems of putting on the World Cup event. Percy Weasley tries to sound important around Mr. Crouch, his boss, but Crouch calls him by the wrong name, “Weatherby”, which settles him down a little. Crouch is concerned and care-worn over the amount of effort it has taken. Bagman, however, seems to think the whole thing is a lark, even the fact that one of his staff, Bertha Jorkins, has gone missing. He’s just excited that the Cup final is happening and is offering odds on the upcoming match. Arthur and the twins, Fred and George, place wagers (GF7).
It seems odd that Crouch, who knows Arthur Weasley very well and who must know whose campsite he's visiting, forgets the name Weasley. Maybe he forgot that Percy was Arthur's son. After all, Percy's personality is quite unlike that of the rest of the Weasleys.
From the Web
Writing by J.K. Rowling on Pottermore: History of the Quidditch World Cup
Pottermore feature: Quidditch collection
Harry Potter Wiki: Quidditch