Germany. Maybe I should qualify by saying that I don't find "fuck" particularly offensive to begin with (American attitudes towards swearwords are strongly defined by its Puritan history).
There is a similar idiom in German ("die Bombe platzen lassen", "letting the bomb pop") but it has a different meaning (i.e. revealing shocking/surprising information) and is different from how we refer to explosions (e.g. "zünden", "detonate") making it sound more like it's describing a balloon than explosives.
I wonder why Americans consider "fuck" more offensive than other expletives, especially considering it's so widely used (and in some social contexts wouldn't raise any eyebrows at all). I guess it falls back to Puritanism again: not only is it a swearword, but it's describing a sinful act -- not simply sexual intercourse but likely sexual intercourse in a very non-Puritan way (i.e. not soberly between a married faithful couple for purely reproductive purposes).
I should also add that English swearwords in German are generally far less offensive than the German equivalents, though even then they're far more socially acceptable. I also think that the German equivalent of "fuck" as an expletive is actually borrowed from English and an artefact of the influence of English language media.
EDIT: I also find Puritanism far more appalling than any swearword or expletive.