It’s a way of saying something is absolutely fantastic and the best at something in the world

Boy 1: I’m playing tennis today
Boy2: Oh you’re Leicester City at that
I’m so good at kite flying you could even say I’m Leicester City at it
by The Wisest owl June 22, 2019
An incest city located in the Midlands the only thing known for in this city is the constant sex the siblings and families have with one another producing an extra finger on all of their hands which is seen as a scientific break through in today’s world. They are also known for being an absolute eye sore of England high crime rate terrible football club no English population and dirty streets everywhere the average house hold in come in commonly known incester is £1 and a pack of quavers a week.
Leicester city you mean incester city that place where all the brothers and sisters have sex with one another? Ew