Snobbish, materialistic, prejudiced, under the illusion that they are better than everyone else. usually offensive. (especially in Scotland and North England)
elegant and fashionable; "classy clothes"; "a classy dame"; "a posh restaurant"; "a swish pastry shop on the Rue du Bac"- Julia Child
If you describe something as posh, you mean that it is smart, fashionable, and expensive. Celebrating a promotion, I took her to a posh hotel for a cocktail. a posh car
If you describe a person as posh, you mean that they belong to or behave as if they belong to the upper classes. I wouldn't have thought she had such posh friends