I worked at a hamburger place while I was in high school. We ran a pretty good operation, so no real horror stories.
I was the night manager, and my grill man took great pride in how clean he could get the grill in the evening before we closed up. It was a very quiet night, and as it was nearing closing time and we hadn't had anyone in for awhile, I told the grill man to go ahead and clean the grill, so we could go home a little early. You guessed it, two minutes before I locked the lobby doors, a guy walks in and orders a hamburger! I peeked around the corner to see that the grill was as clean as the day it was delivered, and I didn't have the heart to get it dirty for one 'burger. So, I took the hamburger and threw it in the deep fat frier with the customers french fries! It actually browned right up! This was back in the days before the 100% beef fad came in, so with all the fillers, it may have been the most flavorful 'burger we ever searved! I don't recall if that guy ever came back though........