The short nickname for the word: Tsundere. "Tsun Tsun" is used for cold/blunt/curt attitude, while "Dere Dere" is used when a person becomes embarrassed in front of his/her lover.
Therefore, "tsun-tsun" is a female character who is usually cold, however the "dere-dere" part is when she starts having feelings for her lover. Or, she is cold to the main character at first, but she becomes lovestruck later.
by Maid-mio November 28, 2010