Envy.

A generally recognized sin in many religions. The thing is, it's hardly a sin, since for sin I consider a VOLUNTARY act that has an evil motivation and/or consequence. But envy can hardly be classified by those standards. Of course, there can be actions which are generated by envy, but there are a lot of instances where the envious person doesn't act or even say a thing. In such case, envy wouldn't be a sin, but a self-suffering, caused by a feeling of inferiority in respect to other person, and the wish for the other to become deprived of some quality or fortune, so he can be inferior too (or, at least at the same level as the one who wishes that to happen).

Let's make an easy comparison with another sin: gluttony. The glutton wallows in the pleasure caused by food, but, unless there is an organic or psychiatric disorded, it is a completely voluntary act. He can choose between giving up to the pleasure caused by food. But also has the choice to moderate himself and have a greater well-being.

The envious, on the other hand, has limited choices. As envy seems to be a passive feeling, he can try to ignore it (such act will not stop the feeling), get distracted with something else, or even try to act upon the subject of his envy (which will worsen things).

When the envious chooses the better course of action (concealing or ignoring his feelings) he does not hope for the best, but actually tries to minimize the damage, which nevertheless is made to him, regardless of what he does.

As it is put on this example, envy is pretty much an annoyance with varying degrees, and pretty much a human trait. Probably has to do something with trying to improve oneself in response to the traits present in other individuals. Sadly, it also fucks pretty much everything in human relationships