Stupidity tax - something you have done that's ended up costing you financially or emotionally.
I'll go first.
I'm in the house one Friday night with dh and the kids. Eldest has a friend over who I offer to drive home. Can't find the car keys anywhere. I nip out to the car (I have form for leaving the car unlocked) discover that not only is the car unlocked but the keys are in the ignition switch on (as in lights and radio should be on but engine is not running). Probably been like that around five hours so the battery is completely dead.
Dh cannot revive the dead battery so end up paying ££ To increase our emergency cover to include home start and £££ for a new battery.
All in all a pretty expensive mistake. This sort of thing happen to anyone else?