Poser, to West Coast American teenagers, means someone who tries to appear to be something they are not.

Example: someone who dresses like a "skate-boarder", hangs out with the skaters, talks like the skaters......but does not know how to skate-board would be called a poser.

It was a word in use in the '80s to denote those who dressed like punks but did not adopt the lifestyle of the punks. Simply put, a poser is a "wanna-be."

The connotation is demeaning but slightly humorous.