Now that I think about it, we did have a game that was sort of a spin on the Slug Bug gag, except we created some of our own rules and we punched really hard. We even had some variant add-ins such as "slug + knuckle rake", "slug + chest poke", "slug + arm burn", or "slug + shin kick", and it wasn't conditioned upon seeing a VW Bug. We were usually stoned out of our minds when we played this.
I wasn't so good at it because it required you to be on your toes and I could barely function when I was stoned, my reaction time was HELLA slow. About all I could do when high was sit there and veg-out to music, but my friends weren't impacted nearly as much, so they usually got the drop on me (but not always).