Bradley Jay: If You Leave The Grocery Store Checkout Line, You Lose Your Place.'

The other day I was standing in a long checkout line at the grocery store and a customer in front of me took his basket and left the line for a couple of minutes to get more groceries. Upon return to the line, he barged his way into his previous spot in line. I was irritated by this as I feel that if you leave the line, when you return, you get to the back of the line. Am I being a curmudgeon? If I left the line, I would rejoin the line at the rear. I feel if you leave the line to do more shopping, then you lose your please in line. Am I right or should I just lighten up?