Butters from South Park is autistic coded, I'M TELLING YOU.
He has trouble understanding the situation he's in sometimes, and when he is nervous or bothered about something he fibbles with his finers, or shyly rubs his feet together as we see in some cases. He is unfortunately not able to see past Cartman's manipulative nature, and is in return dragged into stuff he can't control. More often than not we see him act his age, playing in the backround with other kids, but when he's one of the main kids on the spotlight, you know the episode is gonna have you feeling sorry for the poor boy. He takes things seriously, like when Wendy went to confront him about regecting a girl he didn't like and she yells at him, tellling him he's an asshole, to which Butters calmly reponds , oblivious about the situation, saying that he's not so sure, and that he "Has a body, hands and legs too, certainly not an asshole"
When he's playing, he sings a little song, because he's a happy little fellar, and is known to repeat certain phrases. Some of them are:
-he calls eveyone fellas and guys
-maybe we can say that he's the only one in a few people that call Cartman Eric
-yet again, he sings "Loo loo loo, I've got some apples.." constantly when he's doesn;t have anything to do, and in the Pandemic episode, when he's all grown up, we still see him hum the little song while going to use the toilet.
In the episode Going native, we see Butters get angry to a pretty big level for his usual behavior, even going as far as to talk back to his parents, who we all know are horrible parental figures and would surely ground Butters for the simplest things, but when they are called to school to talk about their son's behaviour, they dismiss it, explaining to him that it was something natural for their family, whatever, I'm just focusing on Butter's outburst. He can't control his emotions, when the kids in the school go to talk to him about how it isn't cool punching a kid and then locking himsel in the bathroom, he walks out, goes on to scream in everyone's face and finally stand up for what he believed about the main 4. We see that he trusts Kenny in that scene, which might just mean that Kenny, the most sane kid in the school probably, understood Butters to a level. I mean in the rest of the episode, Kenny goes on to help Butters travel to Hawaii, to help him overcome his anger, which shows he really wants to help his friend. Aka, this might be a reference to autistic people often masking themselves, and with a serious outburst like Butters', they unmask, and everyone thinks it's not like them, just like how everyone said in the beginning of the episode.
In another episode, we see that Buuters was grounded because he made a 'silly' face in his school picture, and when his mother went out of their house to inform his friends that he can't leave the house, she screams at him for looking at her weird. Poor Butters is confused, saying that that's how his face looks, looking down at his mother witha neutral expression, which still angers her. By tis, we can probably say that he has a difficulty showing his emotions through facial expessions, or maybe the abusive environment he grew in that enforced a "normal" picture for him to follow that was currently slipping up.
BUTTERS IN UNDERRATED!