Maybe this is a different type of mundane costume, but I like costumes that just look like guys. When the anime initial D was popular, I would wear a white T, blue jeans, part my hair down the middle and say I'm cosplaying as Takumi Fujiwara...

What you're doing wrong is not ordering a premade suit from amazon, then chucking it in the bin or a charity shop at the end of the day. /s