Love letter handmaiden card play
You are correct: where appropriate you must target yourself if all other players in the game are affected by a Handmaid card, although the effect of this is not as intrusive as you would think.

The rulebook (pages 19-20) expands upon the Handmaid card, specifically stating:


  If all players other than the player whose turn it is are protected by Susannah, the player must choose him- or herself if possible.


However the rulebook also expands upon each other card in the deck (pages 15-23), and states that the only card that will (must) affect yourself in this case is the Prince:


  If all other players are protected by the Handmaid, you must choose yourself.


The rest of the cards either do not target other players, or are specifically expanded upon to say they have no effect.