Are you (OP) under the impression that you're entitled to a ration of overhead space for whatever you wish to put there? Because I'm afraid you're not. If you're carrying only one smaller item, be it coat or bag, you should be prepared to put it under the seat in front of you. The BA crewmember described may have some room for improvement in their communication style but the underlying action was reasonable.

As to other airlines, Easyjet will (try to) make people hold their jackets until after the overhead bins contain as many bags that won't fit under seats as possible (or all of them), then place them on top. On busy routes in winter, they will take jackets out, ask whose they are, and ask them to be held until all bags have boarded, or placed under the seat.