Some people have evil as a way of life. Some just have it as a job. But others still have it as a tool, using it to serve their ends but able to use it only as far as they need it. They're perfectly willing to do a crime or hurt people if it suits their needs, but when it doesn't, they're also willing to do things the peaceful way.
Basically, the Incidental Villain is a character who technically is a villain, but he only actually does something worthy of a true villain occasionally; most of the time he's not doing anything particularly bad, only when necessary. The rest of the time, he has no problem playing by the rules or being amiable to our heroes. So, half the time the hero doesn't have to worry, because at the moment the enemy doesn't really care to antagonize: They know he's capable of villainy, but they tolerate him because he's not currently doing anything wrong. This kind of attitude is pretty common in sitcoms where the main character is a Loser Protagonist who minds his own business, has no heroic aspirations and would never even consider opposing the villain since he is totally out of his league and could possibly even be his boss. He just occasionally ends up victimised by him when the villain looks for an easy target. In some cases (especially when the world is already their oyster) the only way to stop them is by talking them into taking some preferable action which will be more in their best interests instead of whatever atrocity they originally planned to commit.
Just don't piss him off, get in his way, or otherwise force his hand. Because if he thinks he needs to deal with you, or even think it might be to his benefit, you will regret it, though a necessary part of this kind of character is that he doesn't actively plot against the heroes. He more or less takes schemes as they come.
A Punch-Clock Villain is often this way, due to evil being only a job to him. As does a Corrupt Corporate Executive and other cases of enterprising and capitalistic villains. This character does not go through the HeelFace Revolving Door, because he doesn't actually change sides; he just decides not to do anything evil for lengths of time. If anything, these characters are extremely neutral until they decide to do something devious, and go right back to neutral afterwards. This is a subtrope to Pragmatic Villainy. Even a particularly opportunistic Complete Monster can be this.
Compare and contrast with Heroic Neutral.
- Balalaika of Black Lagoon is this. She has something of a cordial relationship with our heroes, and she only fills the antagonist role on occasion (such as in Fujiyama Gangsta Paradise), and she does things like edit porn when she's not commanding her men, but it is still not a wise idea to cross her or piss her off, as a number of characters such as Hansel and Gretel have learned to their sorrow.
- The Penguin, in the Batman comics, is mostly this nowadays. Officially he's a "legitimate" businessman who owns a nightclub, and functions as a small time criminal operator, sometime snitch, and his club is the place to be whenever the villains of Gotham want to meet or relax. All in all, he himself doesn't really threaten the city much, and is neutral, who helps both villains and sometimes gives Batman info if coaxed enough - unless he's in the mood to try and corner Gotham's underworld, in which case he shows just how deadly and threatening he can be. This happens every once in a while, and the end result is never pretty.
- Depending on the Writer with Lex Luthor from Superman; in some versions he's a Magnificent Bastard 24-7, in others, most days is no more evil than any other Corrupt Corporate Executive in the questionably legal experimental arms business.
- Domina: Law in the city is fluid at best, but Artemis Butler, the leader of Necessarius, prefers to work within it if at all possible—not least because he wrote it. But when push comes to shove, he'll firebomb an entire building full of innocents if he has to. It's just most of the time he can stick to bribes and other political games.
- The appearance of the Queen of Hearts late in Alice in Wonderland isn't directly a threat to Alice's life, as she can be civil and even playful when she isn't displeased and Alice doesn't have anything that she wants. The problem is that her mood is so unstable and so much based on whims and outbursts that a lot of incidents can cause, that she is entirely unpredictable in her insanity, no matter how polite and respectful one is, and therefore it doesn't take long before Alice's life is in big danger.
- Pierce Hawthorne of Community: The other members of the study group know that he's a self-centered ignoramus who can be a genuine threat when he feels insulted or left out, but he's mostly tolerated because they also know how lonely and depressed he can get without them.
- Kirby's occasional antagonist King Dedede, particularly in the games. He's a greedy self-centered jerk, but he's also a king who cares about his kingdom, believe it or not. So, most of the time he's helping to defend his kingdom against monstrous threats and taking care of business, and every once in a while he'll do something like steal everyone's food so he can have a feast on his downtime, which puts him in an interesting space between nuisance and savior.
- Shere Kahn in TaleSpin was reimagined as an Affably Evil Corrupt Corporate Executive, and has no problem with hiring pirates to attack shipping lines that aren't his own or ruthlessly crushing the opposition, but despite being ruthless and cold, his villainy was mostly due to him being extremely pragmatic, feeling ruthlessness was the most effective way to deal with it. Most of the plots dealing with his company happened when one of his employees threatened the protagonists either outside his knowledge (like a rogue scientist going mad) or in a way that he didn't care about (like an inventor whose invention could put them out of business), he almost always helped against the villain of the week when he appeared in their plots, and was even a Benevolent Boss (mistreated employees don't work as efficiently). In the end of most plots where he was antagonistic, he would decide that his course of action was not the best he could do and abandon with no hard feelings, often even choosing Baloo's side because it was the easiest way to get the job done.
- One could argue whether the original interpretation from The Jungle Book applies to some extent. While something of a non-anthropomorphic Egomaniac Hunter that likes to consider himself an intimidating figure, he is suggested to only really hate mankind out of fear of their "red flower" and isn't taken that seriously by other residents of the jungle. He breaks rules of the Jungle as well, even at that however he is merely a normal animal killing for food. The Disney interpretation has some implications of this trait but is rarely shown on screen outside terrorizing Mowgli or anyone protecting him (by the sequel he is so embittered at his defeat he is out and out sinister and malevolent).
- Hondo Ohnaka of Star Wars: The Clone Wars is a ruthless pirate, and will do whatever it takes for profit. This means that while he is perfectly willing to kidnap both hero and villain alike to cash in on their ransom or pillage and/or extort from defenseless people, he'll also gladly help out our heroes if there's enough money in it, as well as abandon any current evil plans with no hard feelings whatsoever the moment they become unprofitable.
- The Brotherhood of Mutants in X-Men: Evolution were less a gang of sociopathic terrorists and more a bunch of antisocial teens being led around by an actual sociopath; once Mystique, and later Magneto, were gone, they couldn't care less about the heroes, wouldn't hurt people or really do anything bad, but just keep to themselves unless they were forced to act. They were practically friends with the X-Men, and had a more Friendly Rivalry vibe to their feud than anything; they helped them all the time, and most times they fought them outside of Mystique's influence were because, despite being not-quite-evil, they were generally assholes, or there was a misunderstanding. However, with the exception of Lance, they adamantly refused to join the X-Men on principle, preferring to mind themselves. In the end, however, they stopped going around wavering on the line between good and evil and joined SHIELD.
- David Xanatos from Gargoyles is a good example. He's an Affably Evil Corrupt Corporate Executive whose only real motivation is his interest: if he wants something, and he can't get it legally, he'll do something illegal, and if that brings him into conflict with the heroes, he'll fight them. If he's not interested in them, he'll leave them alone, he doesn't hold grudges, and being evil isn't his primary concern, just a tool he uses.
- King Julien, of The Penguins of Madagascar, is a prime example of this. Being a spoiled egomaniacal control freak, he's the most common antagonist on the show, with his schemes often being the catalyst for larger plots or being the main threat of the episode. But, despite being something of an asshole, the rest of the animals in the zoo don't have anything more than a casual dislike for him, and tolerate him when he's not doing anything antagonistic, since he's not generally a bad guy, just a spoiled jerk who occasionally screws with people to get his own way.