Green’s Dictionary of Slang

an upper-class person.

1996		J. Byrell Lairs, Urgers & Coat-Tuggers 53: [E]xcept for the poshies in the Members’ enclosure.
1999		Guardian Rev. 1 Oct. 17: So many of today’s ultra-hip dance-music maestros [...] are closet poshies.
2000		P. Howard Miseducation of Ross O’Carroll-Kelly (2004) 86: One of his mates goes, ‘Batter the little poshie.’.