What, that you can remember and posting it wouldnt dredge up painful memories, is the dumbest thing you've ever done.
Mine is when me and my father went bay fishing during a tornado. We were trying to find something we'd enjoy doing together(which we have failed at grotesquely) and we tried to go fishing. We tried sea fishing, and lake fishing, and all had been failures, so we tried fishing in the bay. We got in a rental boat, rented at Polly's boats by the way, the most cheap and shitty looking establishment outside of butt-fuck no where and drove out for 15 minutes, then sat there for an hour, and then it occured to us we should try turning off the motor incase it was scaring away the fish. Then it got windy and rainy, and the rain was coming at us from the side so the canopy was useless, and we were drenched and freezing, and we didnt catch any fish, and then we decided.... fuck it. So we tried to turn the motor back on..... 30 minutes later we figured out how to do that. And apparently we had drifted because it took us 45 minutes to drive back to where we started. And then we decided to free the minoes. And then we dumped them overboard, only realizing at the last moment it was into the motor. And we finally got back onto (relatively) dry land, shambled into the car and declared it the dumbest thing we've ever done.