NEFARIOUS is a word with a huge amount of magnitude.  Words, like many other things, get misused or overused.  Words like NEFARIOUS.  According to Merriam-Webster online it’s very staggering yet very simple:

Flagrantly wicked, impious, evil or vicious.

Flagrantly is conspicuoulsy offensive.

Wicked is disgustingly unpleasant and likely to cause harm, distress or trouble.

Impious is lacking in reverence or proper respect.

Vicious is defined as depraved, impure, defective or faulty

Morally reprehensible.

Unforgivable.

Ever.

I have two words that can simply define NEFARIOUS:  Jeffrey Dahmer.

And, just in case you were wondering, NECROPHILIA is the sexual attraction to corpses.