To perform a sexual act with one's sibling while implying it is both nonsexual and silly.
Once my sister came home from college and sneaked into my room to surprise me as I was fapping to a solo Abby Winters scene and I heard her go "ooh she's cute!" As she placed her hand on my cock which immediately came from the shock/fight or flight response to being caught. She laughed so hard she had to chew on her t-shirt to avoid mom and dad coming in the room to see what was going on, then she put it in her hair and went "I'm Cameron Diaz!".
That is a Bozark.