His vindictive nature often came up for comment among his friends.

Answer: Option C

Vindictive : having or showing a strong or unreasoning desire for revenge.
Timid : showing a lack of courage or confidence; easily frightened.
Obedient : complying or willing to comply with an order or request; submissive to another's authority.
Forgiving : ready and willing to forgive.
Forgetful : apt or likely not to remember.

Antonym of Vindictive is Forgiving