Here are some of the old-fashioned posh or not tests...
How do you pour tea? Milk in first - not posh. Tea first - posh
Do you use fish knives? Yes - not posh. No - posh.
What do you call that bit of cloth on your lap at supper? Napkin - posh. Serviette - not posh.
How do you pronounce 'perfect'? As in the song ("It's got to beeee....") - not posh. 'Perfickt' - posh.
What do you call that lovely smelly stuff you spray on your wrists? Perfume - not posh. Scent - posh.
What do you look in to check your lipstick? Looking-glass - posh. Mirror - not posh.
How do you pronounce 'portrait'? Por-trayt - not posh. Portrit - posh.
....All of which rather assumes that poshness is about pronounciation and the use of some archaic nouns. Is this really the case? To be discussed.