A popular definition seems to be that P.O.S.H was printed on tickets for P&O cruise ships in the early 20th century leaving India. These tickets were for the more desirable rooms which put you on the Port side going out and the Starboard side returning home as it kept you out of the sun and kept the room cool.

However, no tickets have ever been found which had P.O.S.H on the ticket.

Sources:
www.wikipedia.org
www.askoxford.com www.phrases.org.uk

I suggest that the mistake has been made from the full name of the Cruise Liner: Peninsular and Oriental Steam Navigation Company. Maybe a printing error produced P.O.S.H rather than P.O.S.N.C

A more factual defintion still derives from a shipping term which does not seem to be suggested on the previous source sites.

When boats leave a harbour the shipping lanes work to the rule that you must stay to the left hand side like on U.K roads. When leaving a harbour you therefore keep the Port lights of the shipping lane on the left and the Starboard on the right. However, when returning you keep the starboard lights on the left and the Port lights on the right. Hence Port Out Starboard Home... P.O.S.H

I got the definition from G.K mini serie. P.O.G stands for " Persons Other than Grunts In other words guys who are not serving in the frontlines.

Steve won misspelled this word in the spelling bee back in 3rd grade. He spelled C-O-U-P-O-N and while waiting for the principal to tell him he was correct he blurted out "D!" Steve is a dumbass. But you should still vote for him.

pronounced \"pon\". not the same as pon.

P.O.N.: Punk Over Night. Individuals who purchase items like black jelly bracelets, fingerless gloves, Misfits patches, and Sex Pistols t-shirts from Hot Topic and then believe they\'ve joined a movement. Tend to yell things such as \"ANARCHY!\" and \"FUCK THE ESTABLISHMENT!\" at no one without knowing why, but they know they like their spiky leather belt.

Devoid of any original thought processes or ideas. Usually found cruising myspace.com for makeup/hair ideas and bands to pretend to listen to.

Tend to slut around with other PON\'s or real punks to try to earn their respect. They usually don\'t suceed.

Adjective

Post Operation of Nightly Goneness, Use in the morning after partying it up and you are still feeling it when you wake up.

piss of im not telling you ussually used in txt mssgs

Popular RuneScape PKer, known from Team Ghetto, SwiftIRC, World 44 on RuneScape and friends with Hansenmol, P 0 N G O and H e r o x v2