i have a headcanon that berts creator installed a patch to censor berts foul mouth until they could find a way to either completely patch out the ability to swear, or change his personality entirely to be more pleasant. but bert escaped before they could do that so now he's stuck with this censorship. and it feels like a cruel reminder that he will never truly be free from his creator's control, no matter how far away he is from them. a reminder that he would have never been loved for who he was. not by them, at least.
i have another headcanon that could tie into this, too. he was constantly told and shown that he had to be nice, pleasant to be around. but fuck no, he was NOT going to tone himself down just because his creator wanted that. so he screwed on those horns on his head as a way of saying "i'm no angel, and no matter what tries to smother me, i will always be what i choose. it will never change the horns beneath." somethin' somethin' transgender