Green’s Dictionary of Slang

b.o. phr.

[abbr. bugger off v. / SE beat on]

1. go away, leave me alone.

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[UK]Partridge DSUE (8th edn) 34/2: since ca. 1955.

2. (US campus) used as a threat.

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[US]College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 BO (noun) Short for beat on. Used as a threat. Whack off; ass kicking or showing off...And not getting yo ass killed.