wrapped around (one's) little finger
Completely charmed by another person. Usually used with a negative connotation, as if one is under the other person's spell. When I heard that my brother was going to do volunteer work with his new girlfriend, I knew that she had him wrapped around her little finger. When I overheard Ms. Smith giving Ben extra credit, I couldn't help but roll my eyes and think that he had her totally wrapped around his little finger.