Punch Bug or Slug Bug

Okay, I have this long running argument with my friend, Becky, about whether you say "punch bug" or "slug bug" when you see a VW beetle. We need your help in settling this argument.

For those of you who don't know what I am talking about, this is how it works. Anytime you see an old school Volkswagen Beetle (not the new ones, the old school ones) you say "punch bug" and you punch the person you are with in the arm. There are a few variations of this game, but basically it's a car game, designed to keep long boring drives from being long and boring. (Sarah, did your family play THIS game?)

I have another friend, Lori, who says you have to yell out the color of the car when you are playing. (IE: "Punch Bug Yellow" if you see a yellow one.) I used to think this was a stupid variation until I took my first trip with her to do mission work in Mexico. There are like 10 VW Beetles per city block there, so yelling out the color is helpful for everyone to know which beetle in particular you are getting punched for! (That was a terribly grammatically incorrect sentence!)

Anyway, Becky makes fun of me and has for years over the fact that I say punch bug. I, however, have never made fun of her over this, which I do believe tells us all a little something about Becky, right? :) I will also say in my defense that I have never ever said Punch Buggy, and if I had, then I would be totally okay with her making fun of me.

All that to say, which is it, Punch Bug or Slug Bug? Weigh In.