on the edge of one's seat

某人迫不及待。edge of the seat表示‘椅子的前缘’，当人坐在椅子的前缘，代表他很紧张，随时都可能站起来，所以on the edge of one's seat引申为‘迫不及待’的意思

I'm on the edge of my seat waiting to see who has won!
我迫不及待等着要看谁会胜出！