The worst job I had was Life Guarding at a water park for 5 summers. I had to stand in the Texas summer heat 40 plus hours a week from June to August/September, usually with little shade to help out most of the time. Some areas were better with shade, and some spots you were partially submerged in water or you were getting drenched in water. Despite not lifting, it was quite physically demanding and mentally exhausting at time, especially when 90% of the other Lifeguards didn't enforce the rules, many which if you didn't enforce and someone got hurt, you were liable. The 1000's of people that you dealt with who didn't treat you with any respect and refused to listen to you sucked. The 1st summer is the hardest, as they can tell you are new and will try to push you around. 3rd summer on, you don't get phased by much.
Despite the bad, I overall liked the job. You really got laughs out of the stupid people doing stupid things or asking stupid questions. Despite being a hard job at times, I could work as much as I wanted to (I think some state or federal law made it so we didn't get overtime, but I was getting $400 a week on $7.25 an hour, so I couldn't complain too much). Having the job allowed me to save money to go on a trip to Japan, as well as allow me other opportunities later on. Really taught me patience, increased my physical and mental endurance, taught me how to keep a straight face in most situations, how to handle stress, etc.
Best part was while the guests sucked, my bosses were all awesome people, and since I actually did my job to the fullest, they had my back. I still remember a guy twice my size at the time trying to scare me to let his obviously too small child to go on a ride (It was where you swung from a rope). Despite him trying to scare me by making his size comparison known, I wasn't phased. Before he could say anything else, three of my supervisors, all bigger than him, asked if there was a problem. The man took his kid and left without saying a word. They asked if I was okay, and stayed nearby for 10 minutes until they knew the guy wasn't going to come back to cause problems.