Sin

Sin's interpretation depends entirely upon the perspective of the viewer. A sin to a believer of any Abrahamic religion might interpret it as from breaking the vows of marriage to eating pork.
A definition of sin is an act of violation of moral rule. Since morality is entirely dependent on culture, (in Serbia, if one kills your family member, you are obligated to kill one of their family members) and one should not interpret another's culture through lenses of our own. Anything can be a sin and nothing can be sinful.
If one were to interpret a sin through the eyes of a stricter religious sect of people in the world then perhaps almost everything might be a sin, say, Sunni Muslims.
But if one were to view the world through perhaps the eyes of a devout and zealous hedonist who only cares for pleasure - then nothing would be sinful.
Sin is a difficult word to interpret. It's difficult because you can't really draw a definite line across what is a sin and what is not a sin, because, not just because of culture, we ourselves have even a finer exemplary of what is morally right and morally wrong, aka not sinful or sinful.