Ouch my arm hurts

How come every time I come home from being in the car my arm aches??? Hmmmm could it be from playing slug bug and Bingo (yellow cars) every time we go anywhere?  Yesterday My 11 year old sees a VW in the distance and  punches my arm and says "slug bug green", then punches me again and says "I mean slug bug black", then as we get closer to it he  punches me a third time and says "nope it is green".    3 punches for the same VW? Wow he cheats! I'm gonna have to start wearing padding on my arm!