We'll have to just disagree then. In my experience "two for flinching" is a very traditional, widespread game, often dealt by older kids upon younger ones. Its almost a right of passage. It hurts, but its not the same as being beaten up - if the big kids wanted to just beat the younger one up they would, this game is a weird way older kids help younger ones learn to toughen up; its usually done to a younger kid the older ones like. Older brothers for example (seriously allolder brothers I knew growing up, my own included) do this to their younger siblings, older cousins to younger cousins, etc. Heck Bart Simpson has done this to Lisa.
If it is a "rite of passage", it's a daft one, IMHO. I don't know where you grew up, but no one I knew played this game, and certainly not my older brother, or older cousins. And "it's usually done to kids the older ones like", that's not a convincing arguement to my mind. If you like someone you don't bully them.