An example of someone who would be described as stroppy is a rowdy soccer fan who can't be controlled and who is yelling and shouting and being somewhat rude.
Origin of stroppyuncertain or unknown; perhaps shortened and altered from obstreperousBrit., Informal hard to deal with or control; angry, unruly, impudent, etc.
adjectivestrop·pi·er, strop·pi·est Chiefly British
Origin of stroppyPerhaps alteration of obstreperous
(comparative stroppier, superlative stroppiest)