All airlines have bad crew. At the two airlines I have worked/work for I have seen examples of it. Some crew are just like that, I don't know why. You also get those who are having a bad day, not really any excuse and then you get those that occasionally snap when provoked. The latter can be very hard to resist when it's a passenger who persists in arguing the toss when you have politely asked them to do something or who is rude from the outset. This is the only scenario where I have sympathy.
Specifically BA, I think there are some crew who think they are a cut above and in the past they have probably had it instilled in them....but then there are also some passengers who are just naturally intimidated by crew and that might cloud their judgement. A regular example from my experience is if a crew member has left a call bell on or if a passenger accidentally presses a call bell as they move out of their seat, I attend that passenger and ask if they're ok/what can I do .....and they go into a blind panic like they've been accused of something really ghastly.
I'm not excusing such behaviour i'm just saying that it exists at all airlines including mine. There are probably a multitude of reasons for it but I have to say that in general I think passengers are getting ruder. Air travel is getting more stressful and quite often crew are the ones who get the release. But the overwhelming majority of passengers are atleast civil, polite and occasionally an absolute pleasure to have onboard. I think the same can be said about crew.