good 'un/bad 'un/little 'un etc
From Longman Dictionary of Contemporary Englishgood 'un/bad 'un/little 'un etcgood 'un/bad 'un/little 'un etc spokena short form of ‘one’, used to say that someone or something is good, bad etc. Teachers and careful speakers of English do not use this expression He’s a bad 'un. I ought to collect the little 'uns (=young children) from school. → 'un