Bothering Snape

Take him to meet Grawp, saying you'd found a dead acromantula in the Forest
(No, Sir, I don't know how I got there, I was napping and woke up...)

Introduce him to E Bay via 'What I bought on E Bay song'

Sing High School Never Ends whenever he's nearby

Enchant his cauldron to play The Emo Song whenever he uses it

Use medieval technically allowed swear words when addressing him

Play Barbie Song when he walks into the classroom

Use a color changing Charm to make his hair beach blonde

Leave him a fake note from Draco saying that Draco was going to live in the Muggle World

Cast an illusion making it look he's surrounded by snogging students

Put him in a pokeball

Imperio him to wash his hair

Curse him to stand up in the great hall and sing the Barney Song

Make snide remarks about traitors

Curse him with a 24 hour notice me charm

Run away screaming 'it's Frankenstein!' when you see him

Follow him for a day playing mini snape and smile angelically if he turns around, pretending to be busy

Curse him into professing his love to Pomfrey at dinner

Make him think he's gone mad and is surrounded by fluffy pink bunnies