The importance of a place offering some truly tropical vibes, like Brass Monkey, cannot be underestimated in Copenhagen during the low season when there's lack of sun and low temperatures. Inside a concrete building, on a rather empty street, one can instantly be relocated to a Pacific beach with palm trees, surf music and a beach bar.
In the bar, one can find exotic brain-smashing drinks such as Skull Island or The Zombie. Preferably served in a shared skull-shaped bowl with straws for the whole table by surprisingly competent bartenders. If one should get hungry, it's also possible to grab a bite of some exotic grilled seafood.
Expect a very undanish amount of casualness - the cool kitch vibe and occasional limbo seem to bring out the silliness in most people.