I've gone a step further; when it's clear that no PDB service is coming, I ring the call button and ask for a G&T. It usually does the trick (and others are offered drinks then too). If I get the "I'll get you that once we get in the air", I follow up with "Oh, when did the policy change for PDBs ?" sometimes followed by "Not sure if you're aware, but we all get an online survey after this flight, and one of the questions is whether we were offered a PDB, so evidently it's an important service standard to your company". That's the nice way of saying "you're being lazy and we all know it".