Finger up the bum help

So my boyfriend whenever we are having sex tries to put his finger up my bum he always laughs when he does it because he knows I’ll always be a little drama queen about it and make him stop. He would never force it in he just does it to annoy me but i know he actaully would really like me to let him do it. I’m just scared that if he does it he will pull his finger out and poo will be on it and I would literally die 😭😭is it possible this could happen and has it happened to any of you?