Some parent bashing takes place IME but generally only when it's in the best interest of the child. IYSWIM.
So the following are all real instances I have experienced where the parents were 'bashed' in the staffroom...
Children not allowed to participate in any 'fun' or creative activities because the parents disapprove (primary school is for academia only);
Parents not turning up to IEP review meetings, not supporting children's learning, not understanding what the school feel their needs are, not making any contribution to their children's SEN status on any level and then blowing up at the teacher on on parents evening when they learn that their child is not being put in for KS2 SATS because they aren't capable of getting the minimum level 3 and the parents had no idea.
Parents who don't read/do homework/attend school assemblies/attend parents evenings/attend meetings they've arranged etc and then write letters to the school to complain about things they've heard have happened.
There are lots of things that cause eye-rolls and smiles, but most of the time we understand that parents are human and sometimes make errors of judgement, have other things going on in their lives, mistakes and have bad days, but that ultimately, they want the best for their child.
And we hope for the same in return. 