I was just finishing my engineering degree and was interviewing for a few different entry-level engineer jobs. I had interviewed with a smaller firm that was in a less desirable area and the pay was going to be the least of any of the companies I was applying at. They took a long time to let me know and I kept interviewing. A principal from a really cool company from the neighboring state came to my school to interview potential new engineers. My interview well really well despite me only having a bachelors where most who get a job there have a masters. He really liked me and said I would do really well in a small office in the mountains, which sounded like what I would have enjoyed. He said he would have to talk to others in the company and get back to me. Eventually, I heard back from the first company and they made me a job offer. I tried to reach out to the cooler company and they didn't have an answer for me, so I reluctantly accepted the first offer from the less desirable job. I was still in school for a month or two, so I was supposed to work 2 days a week at an intern pay rate then jump up once I officially graduated.
After the first day, I got a call from the cooler company who said they wanted to fly me out for a 2nd interview. I was split on what I should do at that point. I felt like I needed to be "open and honest" with my new employer that I might be interested in another job, so when the president of the boring company took me to lunch, I explained that I had planned to fly out for another interview in a couple of days. He lost it. He was shaking because he was so mad. It was the most uncomfortable lunch I'd ever had. He said he's never seen anyone be so unethical as I was being because I hadn't truly accepted his offer. I explained that I wanted to provide the best I could for my family, and he scoffed at it. After talking a little more about it, I explained that I felt bad about how it had gone and let him know that I would cancel my trip with the other company and stay put with him. He said if I would do that, he wouldn't tell the other guys in the office what I had done and he'd look past it. After lunch, I emailed the other company and explained I wouldn't be able to come out anymore.
Fast-forward two days and he calls me on a Saturday. He explains that he had thought it out and felt that I better find myself another job. As horrible as that was, I tried to hurry and call the other company to see if I could drive out for an interview still and they said they had already offered the position out. So I went from having two potential job offers to none in two days. I was able to find another engineering company in a different emphasis who offered me a job and it has changed my career course since then.
I still think back on that first company and cringe how horrible that all went down, but I'm so glad I didn't work there another day.