Do you want to go have sex?
No
Okay, I’ll give you another chance. How about now?
No
Okay, this is the last time I will ask. Would you like to go have sex?
No
This is your final chance. Do you want to go have sex?
No
I will only ask you one more time. Do you want to have sex?
No
If you do not come home and have sex with me, you will face serious consequences…
No
This is the last time I will ask. Will you have sex with me?
No
Is that a long range missile in your pocket or are you just happy to see me?
…but most of your lines will still only get you a
“You and what army?”
(This might be a case for the SDMB Flirting Academy, but I´ll give it a try)
<explanatory hijack>
Now this, my friend, really depends on the girl. And on you.
Pick up lines do nothing for me, but I love it if someone makes me laugh.
Of course, as I said, he´d have to be my type of guy anyway, cute and all that - but if someone who´s basically interesting comes in with a really hilarious line, we can start a conversation from there. It would have to be really funny, though, and not “excuse me, I lost my phone number, could you lend me yours” or something…
Look, it´s like this: if he´s someone I wouldn´t mind picking me up judging from his looks, and he shows me he´s got my type of humour by making me laugh, it´s better than saying “hey, don´t I know you from somewhere”. By using a really absurd one, he´d show me he knew I knew he was trying to pick me up* and doesn´t take it too seriously, we could have a good laugh and see how things develop.
If the guy´s good-looking but uses a lame pick up line, he´s obviously not my type.
If he´s not my type anyway, the best of lines won´t help him.
But then again, I´ve got a weird sense of humour, so don´t blame me if you do get your face slapped by someone who doesn´t think like me… 
*hey, it´s not easy to pen down the workings of my mind…
</explanatory hijack>
Uncle Sam Wants YOU!
I’m an Army of One. Wanna make it two?