A pun (or paronomasia) is a phrase that deliberately exploits confusion between similar-sounding words for humorous or rhetorical effect. For example: "There is nothing punny about bad puns".
There was a guy in the ocean drowning. He prayed to god to save him. Two boats came and asked if he needed help. The guy replied twice, "No thanks god will save me". The guy drowned and went to heaven. He asked god why he didn't save him. God said, "I sent you two boats dummy".
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http://www.authentichappiness.sas.upenn.edu/
http://www.happiness.co.uk/