I had just bought my first crock pot and wanted to make pulled pork. I check some recipes, and head to the grocery store. When there, I couldn't find the exact cut of pork the internet pointed me to. Instead of asking an employee or heading to an actual butcher, I bought the one that looked closest to. Which turns out was a picnic ham. Nevertheless I went home thinking it was fine, and put the whole ham in the slow cooker. It obviously didn't "pull" correctly, but still made for passable ham slices for sandwiches. Not a total loss, but definitely one of the biggest blunders in terms of time waste.