I used this line at a club once. I was dancing with a group of girls, it got hot so I asked if they wanted to grab some water. They agreed, her friends went back to dance but I told the girl in question (HB8) that we should grab a seat.

We started talking and apparently there was this creepy guy following them around. She noticed him mid conversation and was a little put off. I sprouted, completely off the cuff, "quick, if we make out he might not notice us". She grabs my face and we go at it. Afterwards she commented saying "that was pretty smooth, I'd give it like 9/10"

This just goes to show that you shouldn't take everything so seriously about girls. If you find it funny, even if you have no intention of it working, fucking say it anyway. Maybe it will work. Worst case scenario is you and maybe even she gets a laugh.