I got a few stories on both sides.
For starters, I worked at a movie theater about ten years ago. It was an OK job; didn't pay well, hours were crappy, and the theater had one of those annoying "Movie preview" things running on a loop in the lobby, but if I worked the closing shift on Thursday night I was allowed to clock out and watch the new films in the theater, since the projectionist had to "Check the print."
Anyways, this is about the night I walked off the job. For starters, whoever ordered food and supplies for concessions didn't know what the

they were doing. We had a shit-ton of Raisinettes and pickles but were low on stuff that actually sold (Hot dogs, Reese's Pieces, soda syrup) plus the teenagers they hired as "Supervisors" spent 90% of their time on the clock either in the office or in the projection room.
This happened during that rare 10% of the time when the manager was working. I was at concessions, she was in the back changing out soda syrup bags. A couple comes up to the counter and orders a combo with two drinks, both root beer. All I said was "I need to go check with my manager bec-" he cuts me off and goes batshit crazy. "YOU

ING LITTLE SHIT, YOU THINK YOU'RE FUNNY, HUH?!?! I'LL KICK YOUR SORRY ASS!" For some perspective on this, he was about 5'10", average build. I'm 6'5", 300 lbs, and built like a linebacker. My manager comes up front to see what the problem is. He goes off on her and threatens to kick her ass as well. You know what she did next? SHE

ING APOLOGIZED!!! I was livid. At that moment, I took off my badge, said "I quit" to her and to him I said "C'mon, buddy. Let's rumble!" He ran off, I walked out, and never went back.
Next job I got (Day after I walked off my theater job, in fact) was at a Wendy's. It was made explicitly clear to me I, along with the rest of the night crew, were hired because everyone else who applied couldn't or wouldn't work until 3 AM. In a book, this is called "Foreshadowing."
First night was pretty uneventful, people were learning how to do things, we had trainers with us, all went well. A week later, trainers left and we were on our own. This is when the job got fun.
Two weeks into my job the old, toothless lady who worked the first window and did dishes said "Need a potty break, be right back." This was around 9PM and all the dishes were done, so it was no biggie. Around 10:45PM we're preparing to close the lobby down for the night and prepare for the last few hours, which are all drive-thru service. Kristin, our lobby manager, goes to clean the women's restroom before she leaves for the night. We hear her enter, we hear a scream, and that is followed by the toothless old lady who works the first window bursting into the food prep area like a bat outta hell, screaming "I'm sorry, y'all. I fell asleep on the shitter." Everyone in the restaurant and the guy at the pick-up window all burst out laughing.
About a week after that its around 7PM on Friday night and we're in the middle of the dinner rush. James, our sandwich guy, and Nina, the fryer girl, get into an argument over...something, and James responds by throwing down a spatula, screaming "Yeah, well you're wrong, you stupid

ing bitch!" and storms off. I should note that James is black, as this will become important in a bit.
The lady (who is white, again its important and you'll see why) at the pick-up window can see and hear this going on. I say to her "I'm sorry, I'll see what I can do about getting your order to you." I walk into the back, grab a manager, and for the next twenty minutes (I'm not exaggerating here) Nina, James, and the manager all argue with each other over whatever the

it is that started the argument.
Tempers eventually cool and food service resumes. I finally get the (very patient) lady at the window her food and ask if there's anything else I can get her, to make up for the wait. Her response is "No, but you can tell your manager to stop hiring n******" and drove off.
A few years later I got a job, which I had for five years. The only reason I lost it is because of budget cuts. It was a pretty crappy job, my co-workers were assholes, and I swear that building would suck the life out of you, but the starting pay was $25K a year with benefits, was a 9-5 M-F, and there was room for advancement, so for someone with a HS diploma and previous job experience in fast food and retail, this was as good as it was going to get.
The job: Customer service representative at a PBS station. I soon found out why there was so much "Room for advancement." The people above me were the "Tier 2's" who had to deal with the people who were "Exceptional donors." Near as I could tell, all they gave us was stress and heaping piles of bullshit.
While I have plenty of excellent stories to tell, I'll share with you all one of my favorites. This happened during a pledge drive, when we would show marathons of different kids shows, interjected with call-in's for DVD's of the show and stuffed animals.
Since it was Pledge, my hours were shifted from 9-5 to 7-3, since Pledge began at 7AM. Around 8 AM, I get a call from a mother with a clearly upset child. I can barely hear her over the kid's bawling, so I ask her to speak up . She shouts, in a VERY snooty voice, "Where is Sesame Street?" I explain that we're in Pledge right now and we'll be doing a Sesame Street marathon on Saturday. She responds by screaming "Well, that's just unacceptable. My child watches Sesame Street everyday at this time and I need you to put on Sesame Street." I explain to her that we're a non-profit organization that relies on donations. She screams back "Well, you'll get nothing more from me!" and hangs up. Using my phone's caller ID I do a search for her in our donor database. Imagine my lack of shock when the search turns up nothing.
For five years, that was my life. People bitching about our pledge drives, people bitching about us not having their favorite show on anymore, and more than a few calls from people asking for the phone numebrs of our on-air personalities. One time, right after I started, I gave the extension number to the requested personality without hesitation. Later that day, the personality in quesiton came over to our area of the building and raised hell because "Some pervert called me up and wanted to know if I'd go out with him for some dinner and casual sex." From that moment on I'd politely say "I'm sorry, I don't have her number" and leave it at that.
On the other side, I've dealt with some bad customer service. The one that takes the cake, though, was on Halloween last year. My roommate was home sick and myself and my girlfriend were going out to a party. While picking up supplies, I decided to be nice and stop off at Panera to get him some food, since he's always going on about how good they are. It was a nightmare all around.
Twice the order was given to us in the "Dine in" fashion despite our repeated requests that the order was "To go." When that was cleared up, we went to pay the bill. The total came to $7.53 and I gave the girl at the register $20.53. She hit the button for "Exact payment," took my money, and then looked at me. I said "I gave you a $20 and exact coin change. You owe me some money back." She said "oh, sorry" and the odyssey to get my change back began. She couldn't figure out how much chnage I was owed, even though it was a pretty basic math problem. The total was $7.53 and I gave her $20.53, therefore she owes me...wait for it...$13! It took two employees, a calculator, and a good five minutes to get this figured out.
As we were leaving, my girlfirend loudly noted that the only way someone that stupid could keep their job is if they're

ing the manager. The store's female manager storms out of the back and before she can say a word my girlfriend says "Hey, look. I got nothing against homosexuals, I just hate incompetent service." Jaws hit the floor, people started snickering, and I ushered her out.
As soon as I can, I'm gonna marry that girl.