What are subjects one should not discuss during mealtime?

I know many of you will be unimagined and go for the low fruit and say religion first, then politics second, I hope (big laugh) that you will be more imagined and think along the area of bowel abstraction, your root canal, that backed up cesspool, maybe your dad’s colonoscopy, etc. something that will kill of an appetite. On those lines what should no be breeched when people are eating? Are those types of subjects OK with family, if so, just your immediate family or is it OK to go there when aunt so-and-so is visiting from West Virginia?