I agree with what you say about Oscar Proud, I remember when he declared Oscar Day.
As well as being self-centred he is also a huge dim whit.
I can't help but think that Oscar is Self-centered in moments because of his upbringing by Suga Mama. Seriously look at the interactions between the two; Suga is always antagonistic to Oscar, always belittling him at every turn no matter what he's trying to do or for what reason he's doing it. Yes, the guy is ambitious, but when your wife is a successful vet who's family are either all wealthy geniuses, or stuck up jerks who hate you, and your own family are: a man perpetually stuck in the 70's, a bitterly cruel crumudgeon who has always treated you like crap. Wouldn't you want to make good so you can say "Ha, you were all wrong!" And any time the subject of his childhood is brought up, Oscar is clearly the unfavorite, Suga giving everything to bobby during those times. Now that he's an adult he runs an usuccessful business in the shadow of tycoons like Wizard Kelly; the same guy who beat him in the biggest basketball game of Oscars life, setting the stage for his inferiority complex from then on.
He's the biggest victim of his own ambitions. Honestly; Oscar is the "Meg" of the show. He gets more physical violence doled out to him than anyone else, he almost never comes out on top, in any given situation his point of view will ALWAYS be wrong somehow, and he plays the blithering idiot to his smarter, more successful wife and every third minute shows how damn lucky he was that she took pity on him. From where I'm standing, no one in the Proud Family has it worse than Oscar; with that in mind I think he's got thee right to be a jerk from time to time.
Definitely agree with you on Dijonay; the only friend more toxic and opportunistic that I can think of off the top of my head is probably Dodie from As Told By Ginger.