Posh

According to oxford dictionary,

early 20th century: perhaps from slang posh, denoting a dandy. There is no evidence to support the folk etymology that posh is formed from the initials of port out starboard home (referring to the more comfortable accommodation, out of the heat of the sun, on ships between England and India)

Reference

Oxford dictionaries, (2011)'posh', available at : http://oxforddictionaries.com/definition/posh

 

According to Collins dictionary,

 

C19: often said to be an acronym of the phrase port out, starboard home, the most desirable location for a cabin in British ships sailing to and from the East, being the north-facing or shaded side; but more likely to be a development of obsolete slang posh a dandy

Collins dictionaries.(2011)'posh',available at : http://www.collinsdictionary.com/dictionary/english/posh