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.
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.