My current answer to the question of how I can be less blunt and mean is "spend an uncomfortably long time thinking about all the potential ways what I'm going to say could be interpreted and rethink what I'm going to say until I can't think of any particularly unpleasant interpretations".

A more efficient way to go about it is to

• spend an uncomfortable amount of time conducting a 'post-mortem' whenever you receive feedback that you have been too blunt. Find your mistake, and analyze it.
• accumulate a list of communication mistakes that you make frequently
• spend a modest amount of time checking whether what you are going to say fits the pattern of any of your common mistakes.

Your suggested algorithm tries to never make a mistake. My algorithm is more modest - it tries not to make the same mistake repeatedly.

Once you have made enough mistakes, mine produces results almost as good as yours, with considerably less effort.