Leave, depart, especially suddenly, as in Don't go off mad, or They went off without saying goodbye. [c. 1600]
Keep to the expected plan or course of events, succeed, as in The project went off smoothly. [Second half of 1700s]
Deteriorate in quality, as in This milk seems to have gone off. [Late 1600s]
Die. Shakespeare used this sense in Macbeth (5:9): "I would the friends we missed were safely arrived.Some must go off."
Experience orgasm. D.H. Lawrence used this slangy sense in Lady Chatterley's Lover (1928): "You couldn't go off at the same time...." This usage is probably rare today. Also see get off, def. 8.
go off on a tangent. See under on a tangent.
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.