tsundere

1: being on the surface sharp and sarcastic (tsuntsun) but underneath lovestruck and fawning (deredere); characteristic of a gap between acted out actions and feelings in mind;
2: normally being sharp but at some prompt suddenly becoming lovestruck; hot-cold personality type

そうやって俺のことを気にしつつ、しかし素直になりきれない、そのツンデレtsundereさが今若い男の間で大ブーム！