当我们说一个人“under someone's thumb 在某人的大拇指之下”时，实际含义是形容一个人被另一个人控制了，听从另一个人的指挥。
Don't worry about him. He's under my thumb and will do whatever I tell him.
Some people worry that politicians are under the thumb of big business.
He may have left home, but he's still under his mother's thumb. He broke up with his last girlfriend because she told him to.
当某人或者某事令你觉得特别烦恼、生气或者讨厌的时候，我们可以用 “gets under your skin 钻进了你的皮肤”来形容这种感受。
It really gets under my skin when people park across two spaces. It's so selfish.
I know she can be bossy, but don't let her get under your skin. Keep calm and try to ignore her. She is your little sister after all.