get something out of one's system
get something out of one's system {v. phr.}
1. To eliminate some food item or drug from one's body.
John will feel much better once he gets the addictive sleeping pills out of his system.
2. To free oneself of yearning for something in order to liberate oneself from an unwanted preoccupation.
Ted bought a new cabin cruiser that he'd been wanting for a long time, and he says he is glad that he's finally got it out of his system.
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Source: A Dictionary of American Idioms