WARNING: I can not guarantee the success of any of these lines. I can only state that, in the past, a couple of them may or may not have worked.

Let's start with the classics:

"My name might not be Luna, but I sure can Lovegood" 

"Going to bed? Mind if I Slytherin?"

And then of course there's:

"Did you survive Avada Kedavra? Cause you're drop dead gorgeous."

"I'd like to get my basilisk into your chamber of secrets"

"Save a broom; ride a Quidditch player"

"Want to learn to speak troll? Don't worry I can get you grunting in no time."
(please don't use this in a loud room, it can have the unfortunate side effect of the other person thinking you are calling them a troll)

"Would you like to whomp my willow?"

"If you were a Dementor, I'd become a criminal just to get your kiss."

"Wanna explore my chamber of secrets?"

"My house is called the Shrieking Shack for a reason. I'll show you tonight."

"Hagrid's not the only giant on campus, if you know what I mean."

"You must have given me some Skelegrow, 'cause my bone is really growing right now."

"Did you just use the stupify charm or are you a natural stunner?"

"I don't need accio, to make you come!"

"I don't need aguamenti to make you wet!"

"Have you been using the Petrificus Totalus spell? Because you've made me stiff."

"You don't need to say "Incendio" to light my fire" (calm down gary barlow)

"Baby, are you the Nimbus 2000 cause your sweeping me off my feet!"

~If any of these have helped you out, please leave a review and tell us your success story!~