The classic butt trumpet or weiner jacket. You can also say something about what there farm planet name would be. I'll be back with more.

you can also say "Drop the attitude *name here* your acting like garfield on a monday.

^my friends and I say that all the time.

I know there's something to do with Hufflepufs and finding…or is the insult something to do with Jigglypuff?

I normally say, "You're just a little...Draco, for lack of a better term!"

You can say "You are a sad, spayed little puppy" and make puppy sounds

"You're a toaster" *walk away smugly while they try to work out what that means* OR "YOU'RE A FUCKING ELF!"

Perhaps take a walk off my *insert noun here*

'YOU LITTLE SHIT' :D
or when talking to a group, 'I love you all, guys... except you *xy* I can't fucking stand you.'

"What the hell is a/an *insert whatever the person is*?"

This one works when confronting a group.
"Who are these hideous creatures? Disgusting."

Randomly enter a random room and say, "What the devil is going here" with the best Snape voice you can do. Works every time.