Yay I have many of these!!
I guess the first one would be remembering my way home from the local pub...yea, local...it's around three streets away from my house but for some reason whilst intoxicated I became very lost, so my survival instincts kicked in and I decided to follow the trail of street lights...I woke up not in my bed but in a wooded area next to the M4 motorway.
Another would be the time I decided to do the wiring on my fathers fish pond filters, long story short I electrocuted his fish.
Oh a toaster one....I fancied some cheese on toast but don't have a grill, so I grab the toaster and turn it on it's side, put the bread in with cheese and away we go....I honestly couldn't see the issue with this, but the heat must have went the wrong way or something because I started a fire, unless there was something else in the toaster as that should have worked.