little sistering: the act of gaining interest in something purely because someone else is interested in it, then rapidly losing interest as soon as you get to do it. Sometimes this is followed by the other person losing interest as well.
I was little sistering my boyfriend the other day. He had played skyrim for about a week until I whined that I wanted to play. Once it was my turn I only played for an hour and then lost interest. But since I broke his stretch of playing he hasn't played it since either.