This is a game I have wanted this game a long time but still just not gotten around to getting it. You play as a guy who turns into a superhero and solve mysteries to make your dying TV show popular again. Where it really gets weird is it has Nintendo characters in it like Birdo. You have to find a dildo for Birdo in one mission. Not even joking.
My GOG wishlist is full of games that I wish I had the time and inclination to learn how to play but will buy and then never play because you have to read a novella sized manual first
I think many games I like to play are considered a bit weird, so it's a bit hard for me to pick out the weirdest one... but maybe Ribbit King is the weirdest? From what I understand, it's a golf game but instead of having a ball, you launch a frog around.