Nothing spectacular comes to mind, but I’ve seen a couple of drivers backing up on the motorway after missing their junction, so maybe that.

e: Dumbest thing I’ve done has to be dropping out of university out of spite.

I’m involved in both cases.

1. I was the designated trip sitter while my friends came over and got high. One decided to make brownies and being too impatient to melt chocolate on the stove, put the metal pot in the microwave for a couple of minutes. The kicker is that this all unfolded in front of me; we were chatting and I was too distracted myself to give a second thought about metal in a microwave. Microwave survived, kitchen stunk to high hell of molten plastic handles, and the pot was thrown out.

2. I attempted and failed to seal a leak in the middle of a pipe with teflon tape.

Someone hopped a nearly 6 foot tall by 4 feet deep construction barrier blocking both ends of an out of service escalator, with multiple pallets or replacement escalator stairs stacked all around it. (The elevator was in service right by the escalator)

Anyways, they predictably fell through the massive hole in the escalator and cut their shins to ribbons on the exposed stairs. They then got to the bottom of the train station platform and were bitching about their legs. Eventually, they hailed a police officer just to bitch and whine further about their gouged shins. The officer had the grace to just listen to the guy and not call him a dumb motherfucker for hopping the multiple tall plastic barriers and signs. I was just shaking my head in amazement until my train came.

They’re lucky that they didn’t fall the 30-45 feet down to the train platform by hopping the construction barrier either.

Deny climate collapse

Used new-fangled silicone based lube in the shower when it first came out years ago, without thinking clearly… Ended up with a broken rib and missing teeth. That shhh is slick on bathtubs…

Gamble.

Gamble. Tried it out of curiosity when I turned 19, immediately lost my $20, never entered a casino again.