“Alter Schwede“ does not actually refer to an older Swedish man, but is a colloquial expression, a so-called “Schnack” from Low German. This language is closely related to German and spoken by about 14 percent of the population in Northern Germany. “Alter Schwede” is, however, common as a term throughout Germany.
Without referring to a specific person, “Alter Schwede” is used as an expression of astonishment, with both positive and negative connotation.
In reference to a person, “Alter Schwede” usually expresses an ironic indignation, but can also be meant seriously, as an expression of outrage.
So how did an old Swedish guy end up as a kind of friendly insult? After the end of the Thirty Years’ War, elector Frederick William of Brandenburg recruited experienced Swedish soldiers as instructors for his army to be rebuilt.
As they were particularly good at drilling their subordinates, they were usually assigned as supervising sergeants.
Within the army they were colloquially called “Alter Schwede”, and the expression trickled into everyday speech.
“Alter Schwede, hier ist es aber schmutzig!”
“Wow, it’s very dirty here!”
“Alter Schwede, das ist aber eine schöne Überraschung.”
“Oh my, that’s a pleasant surprise.“
“Alter Schwede, heute möchtest du mich aber ärgern.”
“Dude, you really do want to annoy me today.”