My wife and I have a similarly amusing but totally off-topic game. As we are both very old and silly, we often forget what the last word of our spoken drivel was meant to be. Instead of trying to guess the correct last word, I have taken to adding the most inappropriate word I can think of.
We were resting at our hotel's beach having been scuba diving, and I was enquiring how much drinking water we had in our stock.
My wife answered that she had taken two bottles up the... (she was going to say room)
Our female friend's coffee emanated in two strong brown streams from her nose, when I casually inserted the word arse.