Swedish word meaning 'good houseguest.' It is a custom that started off in the middle ages, when wood was scarce and people would have to take showers in the same bathtub to conserve heat. They would also have sex just to stay warm enough to survive. The practise is still common in swedish neighbourhoods today.
"This morning, the university girls next door came over for a Bjaggenswammker, since it was minus 20 outside!"