Coming back to this topic, I agree with RM's suggestion that
stroppier ought not to remain as a common word. The same applies to
stroppy and
stroppily, both of which are currently classed as common.
Stroppiest is already classed as rare.
For those who don't know,
stroppy is a colloquialism meaning bad-tempered and argumentative. Originating in Britain, it's now quite well-known in Australia and various other places, as Butcherbird notes. However, it's obviously not widely known in the US, which means it is
not common to all major English-speaking populations.
Stroppy is believed to be derived from
obstreperous, and is fairly recent in origin, with the earliest known use in a play first performed in 1950, according to
World Wide Words: "There ain’t nothing clever about answering him back and being stroppy." The playwright, Hugh Hastings was actually Australian, but the play was written in Britain and is about British seamen.
By back formation the word strop has come to be used to mean bad temper - "Don't get in a strop." However this word will remain common because of its razor-sharpening use.