One of my favourite of the Harry Potter jokes! When Ron’s self-spell-checking wand begins to run out of power and starts mis-spelling things, including his own name…

“How d’you spell ‘belligerent’?” said Ron, shaking his quill very hard while staring at his parchment. “It can’t be B-U-M-”
“No, it isn’t,” said Hermione, pulling Ron’s essay toward her. “And ‘augury’ doesn’t begin O-R-G either. What kind of quill are you using?”
“It’s one of Fred and George’s Spell-Check ones… but I think the charm must be wearing off…”
“Yes, it must,” said Hermione, pointing at the title of his essay, “because we were asked how we’d deal with dementors, not ‘Dugbogs,’ and I don’t remember you changing your name to ‘Roonil Wazlib’ either.”
*
“This is your copy of Advanced Potion-Making, is it, Potter?”
“Yes,” said Harry, still breathing hard.
“You’re quite sure of that, are you, Potter?”
“Yes,” said Harry, with a touch more defiance.
“This is the copy of Advanced Potion-Making that you purchased from Flourish and Blotts?”
“Yes,” said Harry firmly.
“Then why,” asked Snape, “does it have the name ‘Roonil Wazlib’ written inside the front cover?”