I did have an interesting experience in the late 80's on an AN A320 when my wife, myself and our 2 sons aged 12 and 14 we seated exit row.
Now my boys were then just a shade under 6 foot (youngest is 6'8" now and the eldest 6'4") and were well versed in aeroplanes, emegency exits and the like.
Cabin manager came back and abruptly stated that the boys couldn't be in an exit row.
On a rebated ticket, not going to argue so they were moved which didn't bother them.
All fine and good to go but before the doors close a family of 3 boards. Mum Dad and a girl probably 12 to 14 who unfortunately for no fault of her own had a major genetic or medical problem and subsequently the cognisant ability of a cabbage.
The dear girl was sat bang in the exit row across from me on the aisle.
After takeoff the CM came through doing the smiley bit while the others did meal service and I got her attention and asked whether there may be a double standard at play without causing any crossover to the family opposite.
Smilingly I was asked what I meant and pointed across.
She went red then white and stormed off. I had been careful not to cross over any angst to the family who God knows had their own problems and were off on a nice holiday. One unhappy CM though.
There were a few grins and nods from other FAs during the flight and I did mention to Ms ex Smiley on the way out the door that I perceived her dual standard as amateur.
Sure the boys shouldn't have been seated there but I didn't know until onboard.
The replacement passengers were a bigger problem as the dear girl wouldn't have been capable of helping herself or even following directions.
I am sure this still occurs but hopefully not here.
Best all
EWL