I burned my fingers pretty badly by ladling stew into a ramekin, while holding the ramekin over the pot because I didn't want to spill any stew on the bench.
When we moved into our house, I didn't know how to prune roses and ended up decapitating three of our roses standard. They're just trunks now, a monument to my absolute departure from common sense.
During a paintball match I hurdled a rope that the staff specifically told us not to hurdle, and spent the next few minutes, um, tactically lying in cover waiting for an opportunity to advance.
I drove to Subway to buy lunch, drove in and then out of the parking lot without even getting out of my car, got back to work, went to get out my car and realised I didn't have a sandwich.