Which words in the English language most reliably mean their opposites?

Hugo Lindgren tweeted:

Is there a word in the English language that more reliably means its opposite than ‘amicable’?

Twitter responses included: “moot,” “humbled,” “nice,” “my friend,” “nonplussed,” “cordial,” “priceless,” “tolerance,” “literally,” “spry,” “sincerely,” “honest,” “pal,” “sure,” and “”Fine” particularly when given as a one word answer.”

My favorite was “spry.”  Is there a word for such words?  Are there other examples?