I've suggested that OPs are looking to be offended, or that they're overreacting, or that their own personal baggage has caused them to react more strongly than the average person would. My number one reason for doing this is that, most of the time, it only causes more angst to the person who was wronged.
For instance, OP writes, "It was really crowded at Target, and I was bumped in the store, and it really hurt, but the person didn't even say sorry!" And the OP goes on to say how upset she is by this, and how she feels so wronged, and should she say something the next time she sees this person. I would reply with something like, "If it was a busy day, it's most likely the person didn't even realize he bumped into you. In a crowd, it's possible to stop noticing when people are running into you, or when you bump into them. I think getting so upset over this is an overreaction, and it's doing you more harm than anything else."
In other cases, I think people hugely overreact to something the average person wouldn't even bat an eye at. Now, it's okay to tell acquaintances and friends that throwing the word "mangy" about recklessly hurts your feelings because your beloved dog has had recurring mange, and it's an awful condition. But going off on someone (even politely) over this is and overreaction, and you can't expect that it's a fair reaction to people who have never even heard the phrase used to describe an actual condition.
I try hard not to minimize people's feelings, but some actions and reactions are unacceptable, no matter how huge the impact of previous experiences. I'm a very easygoing person, but I have a couple of really hot buttons. People push those buttons, and it's very, very hard for me not to take it personally and overreact. I need to know that taking it personally and overreacting is both bad for me and unfair to other people. And sometimes I need to be reminded of that.