Ok I’m intruiged, I know most of these but not sure why…
I would guess pears is because of 離 e.g. li2hun1 i.e. leaving, 離婚 divorce
4 is because it’s similar to 死 si3 death.
The only other one I know is 綠帽子 - but I don’t know why that is!
You are absolutely right about pears and the number 4. To add a little bit more details about 綠帽子, here is a quote from our Chinese Superstitions blog:
"Green hats should be avoided because the saying 戴绿帽 dài lǜ mào (to wear a green hat) is a colloquial term meaning that you are being cheated on."
Hope this helps