His sharp tongue or Fëanor’s talent to insult.

Fëanor the Spirit of Fire was the most gifted of all the Elves in linguistic lore. He could use language so well that his speeches affected those who heard them and inspired them to do different, though not always sensible, things. Thus, being gifted with words and able to use them potently, Finwë’s eldest son was also exceptionally good at insulting others.  Read more