It's an interesting point in developing a well rounded convincing believable character. Would Oscar actually be that convincing if he didn't occassionally show a less grouchy side?
For a character, even a nasty one to work, there has to be something that drives them, that motivates them. And sometimes they need to have feelings too, or else they are not convincing.
Yes you can have out and out villians and such like, motivated by power, or lust, or sometimes the delusional conviction that their way is right. But sometimes there is a danger these characters can be two-dimensional.
Her's an example, last February, I saw a fringe musical, 'Next Door's Baby', twice. The central character Mrs O'Brien came across the first time as quite heartless towards her family, terribly severe with very little in the way of any feelings for anyone. It was not exactly convincing (even if it had been closely based on the script writer Bernie Gaughan's relative), and yet this character was the lead, so it not being convincing had a knock on effect on the drama. The second time I saw the show, the actress had sofened the character during the first act, only really bringing the harshness in later once the audience had warmed to the character. It worked buch better.