See "Kaffee mit Schuss" - German already uses "shot" to mean "a small amount of something put into something else". To order "einen Kurzen" makes reference to the amount of time it will typically take you to empty the glass you get, as colloquial German is kind of used to comparably massive helpings of beer as the pub standard, and many of the harder kinds of liquor are commonly served in comparably miniscule quantities. Or at least, that's how it was explained to me.Originally Posted by Yora