In light of its radical monotheistic theology the worst sin from an islamic perspective is

The worst sin from an Islamic perspective is to associate anything with Allah (polytheism). It is the same thing as believing that Allah has a colleague in His Divinity.

This sin is known as Shirk and if a person dies in this condition, will live in hell forever with no chance of redemption.

Shirk as well as other to be considered major sins are considered crimes to be punished by the Islamic penal code.