Snobbish, materialistic, prejudiced, under the illusion that they are better than everyone else. usually offensive. (especially in Scotland and North England)
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