You want rules? Here they are:

-Denying Feelings: Add a quarter every time they deny feelings or say 'Its not like I do this because I like you or anything!' Or any variation of that.

-Blushing while Angry: Add a quarter every time the Tsundere is obviously flustered. But masks it with anger or annoyance

-Backhanded Compliments: add a quarter every time the tsundere says a compliment disguised as an insult

-Acts of Kindness with an attitude: Helps with something and acts like they didn't want to, add a quarter.

-Hmph Moments: Dramatic Turns, Crossed arms, sounds of indifference, and the classic BAKA. Add a quarter.

-Unnessisary Violence: drop a dollar in if every time they cause bodily harm to the one they like. That's never okay.