Call Draco a "foul, loathsome, evil little cockroach" and punch him in the face. When he asks why the heck you did that, say "Tourette's and muscle spasms" (no offense intended)
Set in 6th year: Ask Draco if Snape gave him the ferret antidote yet. If he gives you a weird look and says it wore off 2 years ago, say, "Really? I couldn't even tell."
(After Buckbeak "attacks" him and he is writhing from his "injured arm") Point out you can't spell "Draco Malfoy" without "Drama" and that he's a total sissy.
Bribe all the Muggleborns, girls and guys, into chasing him in the hallways. He runs, screaming, "Wait until my father hears about this!" Shout after him, "Isn't he in Azkaban?" Pwned.
Get Professor Trelawney to predict that Draco will fall madly in love with Harry.
Tell Draco that you saw Harry looking in the Mirrow of Erised, which shows that seeker's desire. Say you saw them together, holding hands. (He won't know that only the person looking in the mirror can see)
Market "Malfoy stinks!" and "Ferret Boy" badges (courtesy of the Slug Club)
Crash his and Astoria's wedding (this is an absolute must to ensure the lifespan of Drarry)
Most of all...
Say his blonde hair looks gay (No offense, I freaking love this guy, but I had to lol)