What happens if you drop and break a plate of fruit from the Buddha's altar?
Is it bad karma? Well, karma is about intention. If you did not intentionally drop and break the plate of fruit, then there is no consequence for you, from the perspective of karma.
Is it a bad omen? Definitely not. The Buddha did not teach his followers to believe in omens. In fact, we should not cling to unskillful thoughts like superstitious belief in omens.
How should I interpret the incident? All conditioned things are impermanent (sabbe sankhara anicca). Everything that arises, must eventually cease. That applies to the plate of fruit too. If you leave the fruit where it is, in due time it will rot and dry up, even without your intervention.
What should I do? It would be skillful, virtuous and thoughtful of you to clean up any mess that you created, even if done accidentally.
What should I not do? You should not carry remorse or regret for breaking the plate. It's unskillful to cling to remorse. Instead, you should resolve to be more careful next time - that's skillful. You should also not deceive others into thinking that you did not break the plate, as lying is against one of the five precepts.
What happens is the possible realisation of impermanence & the true nature of rupa (materiality).
SN 22.79 says: "Why is it called rupa (form)? Because it is deformed or broken (ruppati), thus it is called form (rupa)".
There was a Thai leader & teacher of many monks named Ajahn Chah. who had a drinking glass. He would always tell his disciples the drinking glass is already broken.
Similarly, it is the true & inherent nature (sabhava) of the altar plate that it must inevitably break (sooner or later).
You should take responsibility.
Someone commented ...
"You will have to pick up the pieces and clean the mess.
That's an answer of a person who has at least such as shame and a feeling of responsibility for his deeds; but nevertheless, it's not the place to play "the cool one" if hurting somebody else.
One may read or listen to "Sensitivity through generosity"
It's a very praiseworthy reaction to feel remorse, even if having unintentionally broken someone else's possession or something another loves. And it is praiseworthy, even if would not having a debt to repay something, to simply use such occasions for training one's generosity -- without long asking who, and why.
Bringing Ajahn Chah here in the right way into this, he said:
"When you see some dirt, sweep it away. When there is something to do, do it. No need to argue around who's duty."
Don't just imitate equanimity (by saying for example "it's just rupa"), or use that as an excuse not to work on the very basics, on defilements.
(Note that this is not given to make anybody a favor, for exchange, trade, gain and bonds but dedicated for release not only from fools but also from debts in this world)