On one of my recent AA flights the seat belt light was illuminated during service and people with blithely getting up and going back to the Lav during service and then acting surprised when the FA didn't want to move the drink cart out of their way to get back to their seat.

After about 10 mins of this cart rodeo we actually hit some pretty nasty turbulence which allowed the FA to enforce "everyone back in your seat" rule and service proceeded forthwith.

The seat belt light was on the entire flight and pretty much no one paid attention to it except for the brief bit of actual turbulance. Quiet annoying.