Single word for being evil but enjoying it?

I know of words such as 'malign' but I am specifically looking for a word that not only expresses evilness/violence but also an enjoyment/choice to do such 'activity', as oppose to someone who does it because they are ordered to or because they 'have to' for survival for example.

Example: The way John handled himself with Jack, he was clearly ______ .

You could use malevolent, malicious, sadistic, or vixenish.

Malicious or sadistic would probably fit your scenario best.

While all four words imply evil/violent, malicious and sadistic both mean taking pleasure in such acts.

Although, the other two words are still good options depending on the context of the sentence.

Is "malicious" the word you want?

From Cambridge dictionary "intended to harm or upset other people".

Note here that harm is stated to be the intent and not stated to be a by-product. Note also that there are expressions such as "malicious smile" where a smile is normally presumed to indicate enjoyment. These suggest to me that the word implies a choice to do the actions and possibly implies enjoyment of them.

You might want to check mischievous (Collins) as well:

causing or showing a fondness for causing trouble in a playful way.

Impish also describes well the connotation you are looking for.

Merriam-Webster has nice examples with this word.

While often used with a sexual connotation, sadism doesn't have to be sexual.

Sadism is a type of behavior in which a person obtains pleasure from hurting other people and making them suffer physically or mentally.