Some people are too scared to make complaints, especially to management. This is why the union is so important
As the union rep at my work place, people come to me with problems and I offer advice and solutions etc.
After being the union rep for several years, I have discovered that some people *are* just a-holes. For no particular reason other than they're just not nice people.
And also, doesn't matter if your dog died, or you didn't have your morning coffee, had argument with your partner, etc. there's no need to bring your baggage to work and use people as your punching bag so to speak.