Stir the pot

A: Why must you always stir the pot and bring up politics at family functions?

B: Because it’s fun to watch everyone get all riled up!

Note: It means “creating dissent and discomfort in a conversation.” This idiom has its roots in the literal act of stirring a cooking pot to keep the ingredients from sinking to the bottom and sticking. By analogy, this idiom implies that someone is intentionally mixing things up or creating some sort of turmoil just to make a boring situation more thrilling.