The Brief: STFO stands for "Stay the F**k out."

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Synonyms: Stay out, Keep away

STFO stands for “Stay the F**k out.” Often used in texting or online messaging, STFO is meant to indicate a warning made from one person to another. For example, if an irresponsible roommate asks to enter your room to borrow your favorite pair of shoes, you might reply, “STFO. But ILY.

Not to be confused with STFU, which means “Shut the f**k up.”