He's mouthing the words along - just like another member of the Golden Trio before him.
On the cream soda line, watch Joey Richter."You can find Harry in your neighborhood bookstore this fall, motherfucker." Another line from Lockhart in the buildup to his monologue.And once I have all that money, I'm going to shrink myself to the size of a fucking mouse! IDIOTS! I'm going to squeeze the Harry Potter franchise for every last, red cent. And in time, a theme park in sunny Orlando, Florida, 85 bucks a head! How about a real butterbeer! 9 bucks, please! It's just cream soda, you FUCKING. I'm going to make these books HUGE then real fun begins! Do you have any idea how much I'm going to make on merchandise? The Severus Snape beach towel! The Hermione Granger toothbrush! How about a "real" wand, you little Muggle bastards!? Well, guess what kiddies: they're just resin! They don't shoot spells! And boy howdy, do they break like fucking twigs! T-shirts, bed sheets, video games, action figures. Even funnier is later when this little interaction takes place:.You've just gotta- takes out a huge knife-take this knife, put it upright on a chair, and SIT ON IT, POTZI!" And it's time for your punishment." "Punishment?" "Oh, it's nothing TOO bad. "I am woman, hear me SMASH!" *stamps feet repeatedly*."WHO DISRESPECTING DA UMBRIDGE?!?" In fact, any scene with Umbridge probably has a couple of these."Didja hear the one about Sirius Black an' Flitwick's li-ul bruvvah?".