"Goyishe" is used as an adjective to describe something that is non-Jewish or is in a particularly non-Jewish context.

For example, eating a pastrami sandwich on rye bread with mustard is Jewish. Putting the pastrami on white bread with mayo is is goyishe.

Anyone who's had a Jewish education would have understood the reference to the 613 commandments. When Martin Gibson said he'd never heard of them, he looked goyishe.

There is also an expression, "goyishe kup," which is Yiddish slang for a foolish person. That wasn't really the context of my usage, but after reading Martin's latest post, maybe it should have been.