FIELD TESTED:
This is what I did...
Well I mixed it up each time, but most of it was pretty much the same.
I already had my first name written on each of them.
I would ask them their name... and say
[ME]: Tell you what... (pulling out a card from my pocket - writing their name on the card and handing it to them) You need a valentine's card from me
[HER]: Awww... that's cute. you're so nice...
[ME]: (insert joke here)
I got 3 numbers today. AND, 6 girls found me and added me on facebook

that was just today - maybe more will add me tomorrow...
some of the jokes I used (off the top of my head)
Yeah, I'm a serial killer so I'm trying to do nice things for people to give back to the community...
Yeah, if I handed these cards out in 2nd grade I would've dominated all the ladies...
etc....
--QB