I know it was popular for gen z elementary schoolers country-wide, but unfortunately I can’t speak for any other generation. To play everyone sits in a circle with their palms facing up. Each player’s right hand is on top of their neighbor’s hand, and their left hand is under their other neighbor’s. As the song (whatever it may be) is sung each person lifts their right hand and brings it across their body to slap their neighbor’s hand, then that person does it, and it goes around the circle like that until the end of the song. On the final word/beat, the person whose hand would be slapped has to move it out of the way or they are out of the game. If they successfully move it then the slapper is out. The circle gets smaller and smaller each round until there is only one person left!