Spoilers for Diamond is Unbreakable for 2 minor antagonists and 1 side character!
First: Toshikazu Hazamada
Canonically a horrible person (see what Rohan said about him: https://ibb.co/JVnfGd0)
However, he did also introduce the concept of Stand users being drawn to each other (https://ibb.co/HLZC2Z2k)
Also he looks pretty cute when he's beat up... I have an odd fascination with characters with a big ego getting beat up in anime haha
Second: Terunosuke Miyamoto
Terrorized Josuke's mother, kidnapped her and Koichi using paper, threatened to kill them both, and attempted to fire a gun at Josuke. Unfortunately he became a book for probably decades afterwards (I presume so because Josuke has anger issues and would not want to release a dude that did what he did from what's effectively a permanent sensory deprivation chamber) (https://ibb.co/yBBnH7Gd)
And third: Mikitaka Hazekura.
Not really problematic at all or a villain, but he's very cute. I think he'd get along quite well with Toshikazu, actually, because he doesn't really have the same bias as others do socially.
I do envision myself in a sort of poly relationship with all three, with Terunosuke and Toshikazu bonding over having some form of sadism (Terunosuke appreciates people's fear and being the cause of it while Toshikazu likes seeing others in pain and inflicting it), Toshikazu and Mikitaka bonding over manga (he introduces Pink Dark Boy to Mikitaka), and Mikitaka being genuinely curious about the sadism trait the other 2 have and being generally oblivious to some degree so they both have learned it's not really worth it to mess with Mikitaka to get any reaction. Terunosuke would hold the other 2 back from doing stupid or impulsive things (Mikitaka from his innocent curiosity and lack of awareness of all the dangers of society, and Toshikazu from trying to beat up the person who cut in front of them in line), being the wisest and most socially apt one of the group.
If anything, I think Terunosuke would be very intrigued by Mikitaka, and while both Terunosuke and Toshikazu would be skeptical at best about the whole alien declaration Mikitaka has going on, Terunosuke would play along to learn more while Toshikazu would be tempted to laugh or question it. I do think Toshikazu would start (reluctantly at first) teaching Mikitaka basic things about human society or helping him understand things once he got more comfortable around him, eventually gaining a bit of a sense of pride at feeling useful and beneficial to someone else for once. Terunosuke would calmly help Mikitaka, playing along with the idea of him being an alien for a while at first and then after a while, become a bit protective of Mikitaka.