I'm pleased you found it funny, as I got hit on the head by a briefcase when the aircraft braked suddenly with some idiots standing in similar cuircumstances and me strapped in
It didn't seem quite so funny with an egg shaped lump and a headache.
The cabin crew should sit people down again (I have also seen an Air France CC member do this very assertively) and if necessary the aircraft should gently stop whilst it is sorted out.
Irresponsible, I'd say, if it is deliberate braking.
This is a known problem in the middel east and the airlines have a duty of care to keep all pax safe.