I’m not saying who is who in this as really want some unbiased opinion.
Mrs A owns all walls that surround her house and has recently painted her sides of them. Mrs B lives next door and has cemented a row of slabs across the top of the wall between the houses. Mrs B did not ask permission but the stones do make the top of the wall look smarter and she has shouldered the cost. Mrs A now has to repaint the wall on her side as the cement has dropped down it (probably an hours job). Mrs A was going to put trellis at the top of the wall but can’t now as the slabs overhang. Mrs A is pissed off that Mrs B didn’t ask permission and had made her feelings known along the lines of “it’s the principle of the thing”. Who is BU?