I would say Person A needs to adjust their sense of entitlement and problem solving skills. Perhaps Person A flies a lot more than I do, but I have had my fair share of flights in F, and cannot ever recall an instance of pax having to take bags out of the overhead to put beneath the seat in front. In a regional jet its easy to justify putting both my bags in the overhead since one is only going to fit on the c/d side and my laptop bag will fit in the A side, which I have never seen full. The remainder of flights, pax either A) go a few rows back to find space B) politely ask if you can move an item or two around since the reason for lack of space is inefficient utilization, or C) ask the FA to put the bag in the closet or if they know of empty spots since you were last to board.