Yekke refers to Jews originating from Germany.
Sometimes used in a derogatory or cynical manner, it refers mainly to their attention to detail and addiction to being punctual.
Used as an adjective, a punctual person would be referred to as being Yekkish.
The origins of this title are unclear, ranging from referring to their short jackets (as opposed to East European Jews who wore long coats) to a conjugation of the Hebrew DaYeK - to be precise.
Only a Yekke would arrive at 2:00 sharp!