Some of you guys have real horror stories.
Elementary school - the PE teachers were nice, but I didn't like PE. I was already very overweight, which made being active uncomfortable, (very probably) had below average coordination and balance for my age, found most of the activities boring (I found school boring in general, but, unlike the regular classroom, you can't get away with sitting and reading your own books during instructional time in gym), and found the physical change from the classroom to wherever we were doing PE that day, the equipment, the lights, the discomfort of exercise, etc. very distracting. It was also a good opportunity for the jerky kids to make fun of my weight and general weirdness. And of course, unlike the regular classroom or the other related arts (with the possible exception of music), if you do poorly at something in PE, it's not just between you and the teacher. Everybody sees it. Still, all-in-all, it wasn't too bad. No real horror stories. My school had after school clubs for all of the related arts. I was in the PE club for two years, and we did some fun stuff with that, including doing sports that weren't covered in class, putting together routines for an annual local talent show and marching in the Christmas parade.
Middle school - I went to a Christian school that did sex-segregated PE, which was probably good. I think we had a few different gym teachers, but the only one I remember clearly was an overweight man who was a bit difficult to take seriously as a role model for health, and, although he wasn't terribly critical, he didn't go out of his way to make the class interesting or encourage/recognize students' effort or improvement. We did some sports, but he also had us doing suicides and stuff like that. Not fun or interesting, and not exactly a transferable life skill for most people.
High school - I picked NJROTC instead of gym. The gym classes looked boring and the NJROTC classes looked interesting and educational (and we got uniforms and shiny things!), so it was an easy choice. We did PFT testing, which I didn't do too well on, but don't remember completely bombing either. It was nice to have physical activities and testing that corresponded to something in the "real world". In general, the instructors knew how to be motivational without being *******s, were still in shape themselves, and were realistic enough to recognize that the majority of the kids in their programs were either uninterested in or ineligible for military service. Most of the cadets were pretty cool, even the ones who took it very seriously and planned on going into the military. The ones who weren't reasonable had no real authority, so if they started being jerky about other people's perceived participation levels or failure to comply with their power plays (e.g., trying to make people exercise after the session was supposed to have ended - and then appealing to the UCMJ if we didn't cooperate

) it was a simple matter of telling them to Foxtrot Oscar or quitting whatever team it was (the totally-not-a-Raider Team, in my case) and joining another, more rewarding, extracurricular activity.
Not gym, but I did discus and shotput on the high school track team. Our first coach was good. He made us work, but his demands were fairly modest, he knew his stuff, and he helped everybody, even people like me who sucked and were never going to make state. Then he got promoted and the guy they brought on to coach discus and shotput was an assistant football coach who couldn't be bothered to show up for most of our practices. Spring football practice was more important. When he did show up, he only worked with the people who were already defending or in serious competition for state titles. Bit of a morale suck! Fortunately, the best people on the team were also good and gracious leaders and teachers, so we did manage to keep things together. My one and only time placing was that year, and it was only because one of the best female discus throwers in the state was on my team and helped me improve.