Haven't had this on BA, but I have on VS, in Upper, and I won't ever forget it either. I suspect the crew were having problems getting the cabin secure in time for a slot so just had a blanket b!tch fest to all the pax to put their shoes on. Not a good way to start a flight.

Coincidentally on another VS flight, again in Upper, the 20 minutes to landing had been announced, and not two seconds afterwards as I got up to stow my cabin baggage, I got .....slapped for not being seated with the seatbelt on. On this occasion I did choose to respond quite firmly that it was clear that I was in the process of securing my cabin baggage as prescribed moments earlier, and that the tone of her instruction was totally unnecessary, to which she responded with nothing but a face like thunder. I imagine she'd been having a bad day at the office, it's the only way I can explain it.