"Half a Horseshoe in my Ass" is when you have half good luck and half bad luck, Indicating you're just as normal as anyone else. Unlike "No Horseshoe in my Ass" which means you're below average or "A Full Horseshoe in my Ass" meaning you're above average. There is also "Multiple Horseshoes in my Ass" which means you are an over-achiever and "Horseshoe shaped void in my Ass"/"Negative Horseshoe(s) in my Ass" meaning an Underachiever.
My friend once said: "I put half a horseshoe in my ass, I'm gonna go to bed and see when I wake up whether it fell out or got sucked in during the night. I'm excited to learn something new, goodnight. I get the feeling I'll be able to predict the weather with this method, we'll see"