Blankety-blank is not a real description of a thing. You drop it in when you are annoyed and you do not want to swear: that blankety-blank machine jammed again. The blank is the empty space where a rude word would go — the same idea as a bleep on television. It sounds a bit old-fashioned and comic now; older speakers and humorous writing use it more than young people. Though actually, it does not stand for one particular swear word. It can hide almost any of them, which is why it feels so vague. You may also meet shorter cousins like blank blank. It is mild on purpose: the speaker shows anger without using the sharp word.

（避免罵髒話時的代替說法）某某的、該死的