The term 'Kill Joy' can be broken down into three crossword solutions: POOP (4 letters), SPOILSPORT (10 letters), and THEOFLIVING (11 letters). POOP is a slang term for feces, which is an unpleasant and often humorous topic. SPOILSPORT is someone who ruins the fun for others by being overly serious or critical. THEOFLIVING is a combination of two words, 'theo' meaning god and 'LIVING' meaning life, so it could be interpreted as someone who takes away the joy of LIVING. All together, these three solutions can be seen to represent someone who takes away the joy of life by being overly critical and unpleasant.