I've actually found that regardless of whether I say anything or not people will still continue to do the same thing. Doesn't matter who it is. Even people I come in contact with on a regular basis. No matter how many times I bring up the same issue with the same person in a respectful & assertive way. I boil it down to these people don't have any respect for me - this also shows in how they treat me in general but that's something else entirely...

Still though, I agree with a lot of what has been mentioned already.