That's a big-time FAA no-no*. I've had that happen on several flights and notified one of the F/A's each and every time where I was also thanked each and every time. Also, I wonder if the PMUA "set-up" (for lack of proper term) of walking the aisles would catch something like this vs "all call" where the F/A's just stand still at their designated positions?

*I would say Bozo no-no but FLIBS is clown enough for me