Try to avoid thinking of a person as Tsundere and think more of the relationship between two people as Tsundere.
Originally Posted by DECK
Let me use an example from the anime Gate Keepers. Ruriko is a nice girl to everyone, except Shun. She's mean to Shun because she likes him but is mad at him because of something he said to her when they last saw each other before she moved. You wouldn't consider her Tsundere, but her relationship with Shun is Tsundere. At the very end of the series she becomes his warm fuck dummy.