In your opinion what is the most destructive emotion?

Revengful hate.

I think fear and hate run neck-in-neck. Despair close behind.

Destructive to self . . . I will have to go with the Z's mention of Despair.

Destructive to others . . . Also, borrowing from the "Book of Z" and say Fear and Hate.

Jealousy

I'm going to agree with fear.

I would rate anger at the top of the list, followed closely by covetousness.

Jealousy as Tiger two wrote.

It can blind a person beyond reason.

Blind hate. Especially when it is something taught generationally.

anger

Uncontrolled anger is destructive and easily leads to violence.