I was fired from my first high school job for not being able to get people to cover shifts I couldn't work due to school events. The supervisor covered me the first time, fired me the second time.
The second job I was fired for taking the working-every-other-weekend thing they told me quite literally. After about 2 months of working there, I missed a weekend shift on one of my "off" weekends. When I returned the calls asking where I was, I was told I could bring my keys back on Monday and that was that. (It should be noted on this one that the HR manager was the business owner's husband, and he blew off the first interview he scheduled with me - one that I raced to from the airport after returning from Christmas break at home. They were jerks.)
The third job I was fired from was a national chain retail job. I broke a dumb rule about coupons (using them as an employee), and when I got caught, I lied about what had happened. Then they told me more information and I changed my story to the truth - I used the coupon cause I'm broke. They asked me why I lied and I said because I didn't want to get fired. Then they all left the room and when they came back, I was fired.
The last one I wasn't fired from, but I was demoted. I got demoted, I think, for disliking the new store manager they hired above me (I was the assistant manager, acted as store manager for 3 months while they looked for someone, and was also bitter about being passed over for the job), whom I perceived to be thoroughly incompetent, but no one ever actually told me why. I didn't fit in with the employees at the new store, so eventually I voluntarily asked for half the hours and got another part time job.
I even managed to get in trouble when I resigned because the store manager didn't see my letter for a few days. She was scheduled to be there when I brought it in, but it just so happened that her sister also had a baby that day so she was gone when I got there. I asked other employees to make sure she got it since I couldn't hand it to her directly like I had planned. Still got in trouble. The next day that I was scheduled, I came in to work like normal and I was taken to the back, lectured for being rude and inconsiderate, and sent home. At least all they could do at that point was take away the remaining 3 or so days I had left on my schedule.