Most people have been on both sides of customer service. We all had to deal with an unreasonable customer, a clerk that clearly didn't care, or perhaps just a profoundly stupid individual on either side. The problem on both sides are people that are just complete assholes.
Customer service people are paid to service customers. Many of them are take this the wrong way. Most of them are apathetic, uninformative, and more interested their phones than helping customers. Someone walks up looking for a product from an empty shelf, rather than check for more, they just shrug and say "I guess were out". At least bullshit the guy a bit, walk to the back and count to five, or fake checking inventory on a computer. Don't be so obvious with the fact that you don't give a shit, at least bullshit a little to earn your check.
On the other side there are loud, self centered customers. People that need printer ink, but don't know what kind of printer they have, or what cartridge it takes. People that see a long line, and try to come right to the front of it. Or the real superstars that come in looking for "that thing I saw on TV", but won't give anymore detail about what they want. If you don't know what you need, don't assume anyone can help you find it. Try bring the empty printer cartridge, or getting in the back of the line, or finding out the name of "that thing on the TV".
We have all been on both sides, at least most of have. The end source of all problem with both sides are people that are exceptionally self-centered, too stupid to ask for what they need clearly, or maybe a lot of people that just don't give a shit. So we need smarter people on both sides, that know the universe is not about them, and maybe we could all put ourselves in the other man's shoes. We just need some sympathy, some courtesy, and some taste.