OK, to a first approximation, think: Pulp Fiction set in Belgium. Or: It's a noir tragic thriller crossed with screwball comedy.
Anyway: Ken and Ray are a couple of British hitmen, ordered by their boss Harry to lay low in Bruges after a killing. ("It's in Belgium," Ray tells us right at the beginning. Because he didn't know either.) Eventually their backstories are revealed, they meet a number of colorful characters who complicate the plot, and a considerable amount of violence occurs.
The funny parts of this movie are very funny. And to its credit, it doesn't shy away from the fundamental evil of Ken's and Ray's profession. (They aren't monsters, but they aren't Hollywood hitmen either.) Among all the yuks, it's clear that they're going to need to pay for their misdeeds, and they do.