Wikipedia defines common sense as “knowledge, judgement, and taste which is more or less universal and which is held more or less without reflection or argument”
Try to avoid using this topic to express niche or unpopular opinions (they’re a dime a dozen) but instead consider provable intuitive facts.
Pretty much anything related to statistics and probability. People have gut feelings because our minds are really good at finding patterns, but we’re also really good at making up patterns that don’t exist.
The one people probably have most experience with is the gambler’s fallacy. After losing more than expected, people think they’ll now be more likely to win.
I also like the Monty Hall problem and the birthday problem.