A monk is a religous figure that often spends time in a temple. A temple is a building that is used for worship or meditation. "Temple tantrum" is close to the phrase "temper tantrum". A "temper tantrum" is when someone loses their temper and is outwardly expressing rage. The joke is centered on the phrase "temple tantrum" because it sounds like "temper tantrum". 
If a Monk throws a hissy fit , is it a temple tantrum ?