Where does a chick come off thinking it is her business to ask how many girls I have slept with?
I've thought about this often and have used numerous lines. I find "the past life scenerio" to work best.
When the girl asks, "how many?" you have to get sad - let your tone change to depressing: "I don't want to talk about it."
She probably won't persist but if she does tell her about the beast you once were. Never give an exact number if the number is over 10 but alude to the fact that you were big pimpin at one time. Talk about all the cheap women and the nights on the town; the bar fights and the blues. Make it sound like you were Bukowski at one point. . . but that point is over now and has left you with nothing but a bundle of regrets. OH how you wish you could change the past, but then again it's not all bad, you learned, you now know what it means to be in love, to think. YOU, my friend had a trial by fire - you walked away a little crispy but you certainy walked away.
It shoulds cheesey and you'd think it would scare them away but I shit you not, this is gold. She'll think you just beared your soul and she'll be turned on with the idea of you being a hard man.
Once, using this technique, I told a girl dated a prostitue and still managed to sleep with her at the end of the night. Don't doubt the "past life" story - it's powerful.