So, since you might know, Sims are supposed to represent us humans in a game-ish, simulating way. Which means, they have similar needs like humans. One of them is the "Social" need. Well, in this challenge, you´ll be completely neglecting this need! In this challenge, every social interaction (with a few exeptions) is a no-go and you have to cope with being lonely and avoid becoming insane. Now to the rules:
Sim:
* The household must only consist of ONE Sim.
* No pets of any kind are allowed.
* Your Sim must have 0 Points spent in the "Shy/Extroverted" bar.

Gameplay Rules:
The following interactions are NOT ALLOWED in this challenge:
* Personal/physical contact with others (that also includes stray animals and the "Talk To Plant" interaction)
* Phone/Computer contact
* Having children ( by wohooing, being abducted, procreating asexually [Plantsims], etc.)
* Building Servos
* Leaving the lot in any way (teleporting, visiting other lots, having a vacation, etc.)
* Calling Services (Maids, repoman, etc.)
* Going to work²

Exceptions:
* You can leave the HOUSE, but only to PAY BILLS and to
* DIG HOLES to get items for money
* Reading books, dancing and daydreaming increase the social need. Since your Sim is technically not talking to another person or pet, it is allowed to do these actions, but I don't recommend it, as it basically destroys the whole purpose of the challenge. (Which doesn't mean you will fail the challenge)

* You ARE allowed, to use the Social bunny as a joker, but only three times. After that, it must be deleted (boolprop testingcheatsenabled true)

* Desperations DON´T count as a social interaction (Psychiatrist, Social Bunnies, Low aspirations, etc.)

End/Completion
The challenge ends when:
* your active Sim dies or moves out
* your active Sim interacts with someone or something
* your Sim leaves the lot

To complete the challenge, you must live a whole life without ever needing to perform social interactions.

Good luck!

[Special thanks to everyone who pointed out any inconsistencies or loopholes in this challenge, you all were a really big help!]

Was just thinking to make "lets play The Long Dark on the Sims 2" where sim is alone on the island with forever winter and need to survive as long as they can. Though sim needs to scavenge another empty lots to find food and better clothes. No electricity and no plumbing, it might be tough.

wow, talk about "social distancing"! "Use social bunny as a joker.." what do you mean? And deleting it after the 3rd time..wouldn't it just keep coming back, since the Sim would still be desperate? So in a constant state of "lost my mind", will they obey any commands...like to eat?

I guess it means when the Social Bunny arrives, you can talk to it three times to get your meter up. Not sure why you'd need to delete it.

Hint for anybody attempting the challenge: writing in your diary increases Social slightly.

When does this challenge end?
Can I talk to my plants?

You might want to add no pets or talking to strays. Sims can keep their social bar full easily with a cat or dog.

Reading novels from the bookcase will increase social. I played a household with a Sim that was being held prisoner (the story involved my Sims having overthrown a dictator), I put a bookcase in his cell so he'd have something to do all day and I noticed his social was going up. Romance books seemed to work best but I didn't spend much time testing it

Daydreaming in a bed will also increase social.

Since the sim can't have babies, I assume when the challenge sim dies. Forever alone...

Dancing to the radio/stereo also raises Social slowly.

does my sim allowed to suicide ? to add more drama on the gameplay

It means that they can be spawned in three times. That means if they appear, you interact with them and then they leave, you've "used" them once. I updated the challenge so now you can always use them if you want.

Thanks for bringing this to my attention. I didn't have the Ultimate Collection at the time I made this challenge, so I simply didn't consider including them in the challenge. It is now updated in the challenge.

I guess you can, "accidents" happen from time to time, after all.
But since the household must consist of only one Sim, committing suicide will kill them (obviously), making them not selectable. The challenge would end there.
But I'm not that strict on when a challenge ends or fails. If you get tired of them or want to do the challenge with another Sim, you can kill the previous one off (or just move them out) and move another one on the lot.
Just make sure to move the grave to another lot if you kill them, so your active Sim won't get scared to death.