Disclaimer: :-(
Chronology: Between Chapters 4 and 5
"So there's this garden gnome - the muggle kind, with the beard and wonky hat."
"Oh, Merlin," George said, looking to the ceiling as if praying for tolerance.
"Let's call him… Brunhilda."
"But that's a bird's name! Call him… Bruce."
"No."
"Brock?"
"No!"
"Bertrand?"
"Shut it! It's funnier if the bloke's name is Brunhilda."
"But-"
"Do you want the version I told her or not?"
George rolled his eyes and gestured for Fred to continue.
"You killed it. I need to start over."
George gave a longsuffering sigh. "Then by all means…"
"So there's this garden gnome – the muggle kind, with the beard and the wonky hat… Let's call him… Brunhilda –Stop mocking me, git -. One day, Brunhilda was traveling the country side with his stupid fishing rod, because that's what muggle garden gnomes do, when he came across a lonely cucumber on the side of the road. Brunhilda was transfixed by the… beauteous cucumber and her… smooth green skin. He sidled up to her and asked 'Hey… Cu-cum-ber often?'"
Silence.
"….That is the stupidest joke I've ever heard. And that includes the one Ron told about the squirrel when he was drunk off his arse at his birthday party last month."
Fred shrugged. "It worked, didnnit?"
"…This is why you have no girlfriend."
"Ah, ah, ah. I beg to differ, dear brother. Women swoon at the sound of my lovely, hilarious tales of jest."
"The name had nothing to do with the joke."
"But you have to admit, it's funny when the bloke's name is Brunhilda."
"You're an idiot."
Fred mimed taking off a large feathered had and bowed low, complete with superfluous hand waving and wrist twirling.
"That actually made her laugh?"
"Harder than McGonagall when we told her we were planning on pursuing careers as secretaries in the Department of International Magical Cooperations."
George raised an eyebrow skeptically. "Really?"
Fred nodded, attempting to look wise and philosophical. "Maybe even harder than Bill when he heard how we left old Pigblemishes. Do not underestimate the power of a stupid joke. Still skeptical, I see," he said, giving George's unbelieving expression a smug grin. "She said that was what made it so funny – said it was 'so pointless and terrible that it's hilarious.' I believe that I've won this round, twinnikins. That brings us to… Alfred 73, George 68. Looks like someone will be doing all the laundry next month, and it will not be me."
"Bert?" George asked in mock joy, staring towards the now bright green owl sitting on his perch. "You didn't tell us you volunteered!"
The owl hooted happily and stretched his tiny wings, shifting from foot to foot, delighted to have been acknowledged.
"Nice try," Fred said, walking towards his bedroom. "Best get started. I've got a load of unmentionables that need cleaning."
Fred heard George make a noise of disgust. Grinning to himself, he shut the door.