You think that it is simply irritation but your toddler doesn’t have the right to act physically against other person whether direct or indirect. That you say, “Tough shit” because you cannot deal with your own child means that you are acting in a shitty manner. There is a difference between a child who is being…

In a just universe the unimaginative parent who cannot manage his/her incorrigible offspring would be assigned to sit in the seat the kid kicks to experience that “mild discomfort.”

Nope.

Riiiiight, and from there it’s “Oh well, social compact, tough shit strangers.”

I feel like the poor middle person should get both arm rests unless there’s some medical reason to share. I (a window person) always cede the center arm rest to the middle person.