I'm not sure if it counts as an injury as such, but close enough...
When I was in my early 20s, I took my eye drops out of the fridge and put them on the bench. I went to the toilet, came back, picked up the eye drops and tried to drop them in to my eyes. Turns out I picked up the super glue. Thankfully, I was really bad at eye drops, so I blinked, and just glued my eyelashes together, but still, it's one of the dumbest things I've done :)