I've heard "going off" for both food gone bad, and people gone bad (ie, who got very angry!). I've also heard "going off" as an expression of something being popular - only in Oz, though.

The funniest I heard was a comment from a tour guide on a tour I did through Western Australia. He'd opened a tin of beetroot slices as a condiment at lunch (why DO Australians put beetroot on "everything"?!) and no one took any. He looked at it part way through lunch and said, sarcastically, "I see the beetroot's really going off." No one said anything and he felt the need to explain: "I mean, it's not going off or anything - it's not popular...." I had a good giggle over that one! in trying to say it wasn't popular, he realised that he'd suggested it was going bad...eh, maybe you had to be there.