A new mother came up with the ultimate office prank against a co-worker consuming her coffee creamer from the communal refrigerator.

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Reddit user Phantom0591 refilled the conventional-looking coffee creamer bottle with her own formula.

"To whomever has been enjoying my coffee creamer all week… Surprise!!! You've been drinking my breast milk. Hope you enjoyed," she wrote in the post titled "Stay away from the coffee creamer at work."

The lactation lesson was all in good fun.