Learn English – What word is used to describe always using words that mean the extreme

I thought of a third possibility that covers the transition part.

Capricious: governed or characterized by caprice : impulsive, unpredictable.

If I think of something better, I obviously have no compunction against adding another answer. :)

A curmudgeon is someone who is bad-tempered and disagreeable - so curmudgeonly?

A contrarian is someone who takes an opposing view, especially for the sake of being difficult, contentious or in opposition to the generally held view. This could also be used as an adjective.

A troll is, in a certain context, someone who says something deliberately for the purpose of insulting or upsetting someone. (Thanks RegDwight AAA, and no offense intended to Norwegians).

My British friends and relatives might also say that such a person was "playing silly buggers" (or beggars).