To be keen on doing something

Keen on Cake
I’m keen on cake. Don’t touch my cake. IT’S MINE!!!

To be keen on doing something is a common expression that means you like something or someone, or you like doing something. For example:’ I’m keen on Brad Pitt.  I’m keen on carrot cake.  I’m keen on watching football.  You can also use this expression in the negative:  I’m not keen on chocolate ice cream.  I’m not keen on rollerblading.