I think the answer to your question Frederica, is a good dictionary. This phrasal verb like many others has multiple meanings. Here are a few: - You really shouldn't play around with a loaded gun; it might go off! - I shouldn't have left that milk on the kitchen table in this warm weather. It has gone off. - Have you seen Mike? We were going to go home together. - No he's already gone off. - is Sara still going out with that guy she met last week? - No she's already gone off him. - That's annoying; I was going to have a shower, but the water's gone off. - He used to be a really good actor, but he's gone off a bit in his more recent films.

In addition to the great examples that were given in the other responses, I just wanted to say that as a New Yorker from the younger generation, this is actually a common slang term. I don't know where you heard this, but many young New Yorkers say "she went off on him," for example, to say that they got very angry and started to yell at the other person. So when I first read this, that was actually the first meaning that came to my head, although it is very coloquial and informal. Maybe that helps and/or is interesting for you!

That phrase isn’t commonly used. There are a variety of contexts possible. In addition to the examples above, on could use it for someone who has gone a bit crazy. E.g. “After years of stressful work, Paul has gone off the deep end”. Yet it’s rarely used in this context

No, it’s different. It can mean “to go bad” (e.g. fruit, milk), “to explode/begin to sound” (e.g. a bomb, fireworks, an alarm). It can also mean “to leave” (to walk away in some direction)…

So I guess, yes—that is one of the meanings (but not necessarily the most frequent one).