It's when you and another male/female gets funky and the male participant decides to place his meat between the butcheeks and applies, mustard and ketchup next to the sausage and puts ristede oninons (Danish garnish) on top like a garnish.
The goal is for another male or female to suck off the garnish without letting the ristede onions get inside the buttwhole.
There you go the Copenhagen Hotdog.
- "Dude do you wanna come over later so we can practice the Copenhagen Hotdog?"
- "Sure"