The Capulets conclude that the law would not be on their "side" should they admit that the openly "bit their thumbs" at the Montague men.
What sort of law was there against this in the time period that Shakespeare is referring to? Could it be circumvented by simply lying about the gesture or its recipient? What was the punishment? Was it common?
What significance did thumb "biting"/flicking have? Are there any other references to it in other works or common history?
More can always be said if anyone would like to address Italian honour and duelling culture (as portrayed through the lens of that hack from Stratford-on-Avon!), so if you'd like to write up your own post, please don't let this linkdrop stop you.
While we wait for fresh replies and new perspectives, OP, u/Georgy_K_Zhukov has anticipated just this question, and bites their thumb, sir!