I saw a very fine player turn this cube and immediately he grabbed a pencil and began to score it.  His opponent said, "What are you doing, I haven't decided yet."  And the player said, "Oh, sorry, I just assumed you were dropping.  My bad."

Of course, it was a big take, not really even a cube, but people have a tendency to play far too cautiously when they have a lead, and the bluff of grabbing the score sheet worked well, as his opponent quickly dropped the cube.

Did the doubler break any rules?  Probably not.  Were his actions "gamemanship" or "poor sportsmanship?"  There is a fine line between the two, and the answer lies in what your personal values are, as I know of no clear rules that prevent this kind of bluffing.  I do know that I don't like it, and I don't think this is the way the game should be played, except in "friendly games" where the players know each other well and have a history of kidding around.   

But again, actions like this are very hard to control or define.  Is it poor sportsmanship or bluffing if you double very quickly and emphatically hoping to intimidate your opponent into dropping?  Is it poor sportsmanship or bluffing if you agonize a long time thinking about whether to cube a position that you know is a huge drop but you are trying to get your opponent to think that you're not even sure it's a double?  I make sure to keep a "poker face" even when things are going very badly for me, as I don't want to alert my opponent that he should be considering a double.  It's all a very fine line, so be careful and realize that there is gamesmanship and bluffing in backgammon, just like poker.