Never had set code words. Usually just, 'I'm going to bed' or 'good night' would be enough. Or there was something broken in the bedroom (bed frame, lamp, anything...)that needed both of us to fix. And 'I need a nap' was good too.

Worked when the kids were little, then they were teens and caught on...... quite often we'd get 'ewwww' or 'gross'. Now thier older the reactions have stopped. lol.