We don’t punch for those, but if the plate is from a state not close to ours, we yell, “Landed Alien Out of Zone!” We yelled “Landed Alien Way-the-Heck Out of Zone” when we saw a plate from Alaska.
It certainly goes back to the 1940S as “Padiddle.”
Never heard of it until about 10 yrs ago.
Grew up on the East Coast (DC Suburbs, Vermont, Upstate NY) in the 60’s and 70’s. The family went on a lot of road trips.
Slug bug - sounds cutest. (Northern California, 80s-90s). Continual punching till the punchee said the color of the car, resulting in lots of “Rrgh! black! red! blue! yellow! green! white! etc…”.
Sometime in the early 00s, bugs overran my city, so we switched to Out of State License Plate for a while. Then we stopped playing.
Slug Bug, Alaska, 1970s. Just one punch, but had to be qualified by the puncher saying to the punchee “no slug bug Backs!”
Slug Bug, one hit per bug, color is usually mentioned but is not required. 80’s/90’s Northern Idaho. What’s this “no slugs back” crap? You wait until the next bug to smack me, there are no freebies in Slug Bug.
My folks and I did Squeeze Bug instead of smacking each other. The squeeze was that horrible goose above the knee that makes me twitch and squeal, I often thought that I’d rather be slugged.
One headlight - smack the roof of the car and yell “Beer Me!” Which was dumb because we never had beer when we were young enough to play.
Cop lights - “Sex lights!” Everyone else in the car joins in for, “Someone’s gettin’ screwed!”
I never played it and never even heard of it until I was a junior in high school in western New York, circa 1986. A teacher of mine told the story of a cross-country trip he took with a friend just after they graduated from high school, circa 1970. As they were driving along, the friend yelled “punch buggy” and punched my teacher as hard as he could while he (the teacher) was driving. That must have been a fun trip.
I learned it as slug-bug. Twin Cities, late seventies.
Red or convertible would get you 2.
Red convertible is 3.
We played pretty hard, and bruises were not uncommon. one time we went to Mexico in the early 90s and had to suspend all slugbug until shoulders healed.
We also played Car-Truck! (puking sound). Just the puking sound. No violence.
My son has the benefit of learning from the Irish cousin that stayed with us two summers. They play Yellow-Car! like slug bug in Ireland. So my son brutalizes me with all kinds of vehicles.
Slug Bug
Midwest 1980’s
If the person was mistaken, you got 2 punches back.
Punch buggy. No punch backs (mom wouldn’t allow it.)
Course, we actually drove a VW bug at the time - so the first one was like calling shotgun. It was a race to not be the loser.
Of course, if we both called it - the first one to yell out the color got it.
If we both said it at the same time - it was followed by “jinx one two three - not it! you owe me a coke!”
Or something like that. I dunno. We owned a VW bug AND a VW van. My dad was a teacher, my mom drove school bus, we lived in a tourist beach town. I’m surprised I wasn’t named moonglow.
totally off topic: anybody else ever have to ride on a board suspended between the driver and passenger seat in the front of a VW van? Now THAT was safety . . .
Grew up in northern Virginia in the 1960s.
Never heard of ‘punch buggy’ or ‘slug bug’ or anything like that until reading this XKCD.
But, did you know what a pididdle was?
Slug - a - bug.
Northeast Wisconsin, 1990s
Yes, slug backs are allowed, if the person doesn’t call out “no slugbacks!” right away.
Nope, never thought of that method of inflicting extra pain… 
It was Slug Bug in 70’s Detroit Michigan. “Buggy” doesn’t even make sense. Any car is a buggy, especially if it’s drawn by horses. In my family, we weren’t allowed to slug each other. We just said “Slug Bug” and stated the color. No other phoney made up rules, and there is no slugging back in Slug Bug. You’re thinking of Tag.
I finally realized why I never heard of this: I was an only child. No one to slug but the parents and I wasn’t about to do that. I did know what a pididdle was because my dad would say it but it didn’t involve any hitting.
Cleveland, grew up in the 80s, “Punch Buggy” followed by the color, and punchbacks were allowed unless you specifically said “no punchbacks”.
And the “new Beetles” don’t count, damnit, but I’m having a heck of a time convincing my nieces and nephew of that.
Punch Buggy, no color NYC '70s.
Late 1960s/early 1970s. Tennessee and Mississippi.
And we didn’t call it any of those things. For us it was Spud Magoo.
You saw a VW, you yelled “SPUD!”
You saw a red one you yelled “SPUD MAGOO!”
Also, there was no punching. We kept score. One point per spud, three points per spud magoo.
Oh, by the way, “Bump!”
Punch buggy spring, 1970 in route from Texas to Florida. I was 6 with two brothers aged 12 and 5. This game sucked for the younger two of us. There was no punch backs. Within a few years family rules for the game evolved into points rather than punching although we’d play punch buggy with other kids our age when out with other families or cousins.
1 for a run of the mill vw bug
5 for a convertible or bus
5 for some rare color I’ve forgotten and
5 for a dented driver side front fender.