Affably Evil is when a villain is polite, friendly and genuinely kind, even while plotting evil. Good Is Not Nice is the inverse: characters who are rude, unfriendly, or mean, but still firmly on the side of good.

They won't kill (if they can help it), nor would they turn a blind eye to human suffering. They are always willing to go out of their way to save the town and complete strangers. When the call comes, they answer it, usually with little protest. They often help people in need who can't pay them back. In almost every way, they act like the Ideal Hero, except...

...they are asocial and sometimes downright rude. They may refuse to explain anything or listen to anyone. They actively refuse offers of gratitude, friendship, love, and/or support for their own emotional problems. Yes, they'll always be there for you. But they don't always seem to like you.

There are a few reasons these people may act like this:

1. They may want to be selfish and arrogant or just unbiased to either side, but their morality keeps on getting in the way, even if it is to their detriment. They may put on "jerkass/bitch mask" to try to counter it.
2. They do consider themselves as better than everyone else, and their attitudes range from Smug Super to Insufferable Genius to flat-out prick. After all, it is difficult for them to be nice to people when they do not even respect them. However, they still feel compelled to help these lower creatures on a regular basis.
3. They are natural loners. Their senses of duty force them to perform heroic acts, but they do not consider chitchat or politeness to be parts of their obligations.
4. They may want to be affable people, but they believe that being nice does not always get things done, and that doing good can require them to be harsh or cruel sometimes, particularly if they have to teach something (this may be an intermittent effect, applied only when necessary; contrast Beware the Nice Ones, where such outbursts result from break-down. On the other hand, emotional trauma can coincide with the realization that nicety won't cut it.).
5. They cannot afford to let others get close to them because their enemies will use others against them.
6. They might wish to be nice but live so far outside normal human experience that they have no idea how to go about it; similarly, the hero might be autistic, or a non-human alien.
7. They weren't always like this. They had friends and/or even romantic relationships, but time kept taking their friends and family from them. So, at some point, they decided never to have any relationship deeper than acquaintance.
8. The world the heroes live in is operated through cynical ends, so Strict Good Guyism does not work — either in the eyes of the author or in a literal in-universe sense.
9. They operate on Blue-and-Orange Morality, their unpleasant actions can be seen as "nice" in their worldview.
10. They intimidate enemies through harsh demeanors.
11. They used to be a villain before warming up to the heroes. While they may have renounced their evil ways, they retain their bad attitude.
12. They may be good, but SOOO fed-up dealing with people who don't know and won't learn, the constraints of working within a dysfunctional system, the hostility of people who resent their heroic reputation, etc, that they've become... abrasive.

Note that when handled well, this can create an interesting, complex character. When done poorly, you can end up with an Unintentionally Unsympathetic character or even a Designated Hero. Furthermore, a "good" character with an extremely abrasive personality and/or deplorable actions may find themselves targets of Ron the Death Eater and/or Never Live It Down.

Compare Noble Demon, who will likely fall into this if not too morally ambiguous. Often a Knight in Sour Armor, Mr. Vice Guy, Jerk with a Heart of Gold, Jerkass Woobie, or sometimes just a Jerkass who does good things. The term Anti-Hero is sometimes used to cover this trope. Sister trope to Creepy Good. Naive newcomers may be surprised to learn they are not the idealized hero everyone thinks they are. The hero's meanness will result with him becoming a Hero with Bad Publicity.

Why Light powers can be the Holy Hand Grenade even when Light Is Good.

Lawful Good versions of this trope may be strict, humorless and serious. In other cases, they will put more emphasis on "Lawful" than "Good". This is fairly often used as a personality flaw for The Paladin. Chaotic Good versions will often see politeness and good manners as useless rules and are only concerned about doing good.

See also Hidden Depths. Also see the Knight Templar, who goes beyond merely not being "nice" into darker territory.

Contrast Good Is Not Dumb. May overlap with Good Is Not Soft, but the key difference is that a character can be nice but ruthless, which makes them Good Is Not Soft, or they can be mean but not necessarily ruthless, making them this trope.

See also Affably Evil, a trope that could be called "Evil Is Not Mean." Contrast both with Faux Affably Evil, for when the villain is a far bigger asshole than any hero under this trope while acting superficially nice.

This is what the Knight Templar and the Obliviously Evil tend to think they are.

Examples:

• Anime & Manga
• Fan Works
• Literature
• Live-Action TV
• Video Games