The suicide king is the name for a playing card. It's always the "king of hearts". The king is depicted with his sword going behind (or through) his head. You'll find this name used most often in a home poker game. A usage example: "Ok, the game is high chicago and the suicide king is wild".
All of the face cards of playing cards have proper names going back hundreds of years. The proper name for the king of hearts is Charlemagne