"Other." Multiple of the above- anger, comedy, just do, but when I don't it's occasionally because it would be rude to do so- mixed with "because I know the words and see no compelling reason not to use them". Sure, someone might be offended by "fuck", and if I know that I'll try to avoid upsetting them, but in general I use them because dammit, they're words too and I should be allowed to use my words.