勝手 expresses acting according to one's own will, often selfishly.
COMMON PATTERNS:
- 勝手に〜する (do ~ without permission)
- 勝手な〜 (selfish ~)
- 自分勝手 (self-centered)
- お好きに勝手に (as you like)
MEANINGS:
1. Selfishness: 勝手な人 (selfish person)
2. Without permission: 勝手に入る (enter without permission)
3. Kitchen area (historical usage): お勝手
Note: 勝手にしろ means "do what you want" (I don't care).