Not only eating in someone's car is rude.

How about someone cutting her finger nails inside your car? Yes. that happened to me (long time ago, before Grab introduced Passenger rating system). Of course I didnt want to sound her immediately (and it was an elderly Indian woman BTW)

I took a photo of the finger nails she left on my car seat and some on the carpet , and send it off to Grab.
Then I don't know what happened next lah.

I have also encountered Banglas just finish smoking upon my arrival at pickup point , even when he got into my car I could smell the cigarette smell. Of course I politely said to him - "bang, kamu hisap rokok tadi ya? I bukak tingkap sekejap" and he agreed.