One of the world's great pickup artists, Mystery (aka Erik Von Markovik) has pioneered a controversial practice known as negging, making a "subtle-yet-negative statement that puts a target off-guard and makes him/her question their perceived value" e.g It's your lucky day--I'm on the rebound, and my standards are low.
According to Mystery, the response to a successful neg is laughter, but it also increases your target's susceptibility to advances. While anecdotal evidence suggests negging works, proceed with caution.
Here is a list to get started with...
What is a nice boy like you doing with a face like that?
I may not be the best-looking guy here, but who are you to be picky?
I sacrificed my dignity to come talk to you. The least you could do is say yes.
I thought I'd come over and give your self-esteem a boost.
I'm a sweet guy, and you clearly have a taste for sweets.
I'm feeling charitable. Wanna go out sometime?
It's your lucky day--I'm on the rebound, and my standards are low.
You looked better from across the room, but now that I'm here I might as well talk to you.
With a little surgery, you wouldn't be half bad.
Beauty is only a light switch away.
You're ugly, but you intrigue me.