Wistahe
blackle moriwhat's the deepest game that two average people could feasibly play entirely in their heads? e.g. some people can play chess in their heads, but I wouldn't call those ppl average
witch hat hacker 
@suricrasia flirting?
goaty goats (she) 
@suricrasia as someone who knows very little about the topic, i'm going to say tic tac toe. only 9 squares to keep track of, very simple mechanics
esclear@suricrasia
What about quantum quartet?
That's basically quartet (also called "go fish", I think), but the cards and categories are made up on the fly.
So if I asked you whether you have the "emacs" card of the "text editors" book, I would have established that there is the "text editors" category and that "emacs" is one of the four cards therein, no matter what your answer was.
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@suricrasia
One has to keep track of the game state in ones head. If someone creates a paradox (e.g. creates a fifth card of a category), they loose.
There's a somewhat longer explanation at https://github.com/jessijzhao/quantum-quartet/blob/master/rules.md .
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Léo :Chaos:ω:Chaos:@suricrasia anything revolving around roleplaying could get quite complex without being too difficult 
Maya@suricrasia Probably a game having 7+/-2 positions, so something like tic-tac-toe, lights-out, or wordle.
@suricrasia You could probably push that to games like Connect 4 if you teach people how to encode the game state using trinary numbers, but that's not really an average person idea.
Kneebiter@suricrasia Either of the games known by the phrase "I'm going on a trip".
Csepp 🌢@suricrasia Maybe roleplaying, or something like questions only?
Haelwenn /элвэн/ 
@suricrasia Well, Word chain is an obvious one