This is probably not the dumbest thing I've done, but I've gotten the most teasing about it. Took some friends on their first winter backpack about 6 years ago. I brought cheese to eat for lunch and butter to put in the dinner pot. Since I wanted to keep them both in the fridge at home until I left, they got packed last and went into different outside pockets of my pack. During the hike I went to eat some cheese and opened the wrong pocket. Since the butter and cheese were the same color and I'd cut them into similar sized chunks and their consistency is very similar to 20F, I didn't notice that I'd picked the butter until I'd taken a very big bite of it. I chewed it and swallowed as my friend took a picture of my face. Since then I'm not allowed to bring the cheese because I can't be trusted to know the difference between cheese and butter.