gross-out session
gross-out session {n.}, {slang}, {avoidable}
A verbal contest between teen-agers in which the object of the game is to see who can be more disgusting or vulgar than anybody else.
When Jim got home he found his two teen-age sons engaged in a gross-out session; he bawled them out and cut their weekly allowance.
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Source: A Dictionary of American Idioms