With my parents it’s really easy for a fight to break out, although typically we don’t fight at a holiday dinner. If I wanted to ensure a fight I’d probably have to lie. Here are some things that aren’t true, but my parents would not be able to contain themselves:
If I said I’m voting for Trump it would start an argument.
My husband is going to quit his job. My parents would freak out.
Actually, back to Trump, if I just say the Democrats are going about thing wrong to get rid of Trump, which I do believe and have fought with my parents before, that would be enough.
With my husband’s family I’d just have to say to my SIL that I didn’t understand something she said, or disagree with anything she is saying at the table. She talks a lot (I don’t mind that she talks, I do too) but she likes to be right. The only problem with fighting with her is if the fight is bad enough she won’t talk to me for 5 years or more.