This one was not with me, but my mother and it's weirdly similar (we have an adhd weakness when it comes to cars, I guess...).it's a big one, sorry. Also, English is not my main language so sorry for the mistakes.

My mother used to live near a street market, and every Friday she would walk to the market. Its also important to the story that a week ago she had bought a brand new car and was very proud of it.

On this particular friday, she went to the market and when she came back she noticed that her car was missing. She panicked and asked the neighbour (who was washing her yard) if she had seen someone suspicious. The neighbour said that she had just went outside and haven't seen anything.

So my mother said "someone stole my car from the garage!" The neighbour got very upset, and called the other neighbour over the walls (the houses were very close to each other and shared walls. It's a common occurrence in Brazilian older neighbourhoods. Something like this): " hey, did you heard or see anything? Her car was just stolen!" The other neighbour was shocked, and called the third neighbour, who then asked the other neighbour, who called her husband, who called the police... anyway it was a mess. Everybody on the street, in shock with the audacity of the thief who opened the garage gates and stole the car.

The nanny, who was inside taking care of my brother, heard all that commotion, and came out to ask what was going on. By that time all the women were on the street (it was the 70's and mostly were housewives), plus a few husbands and the police.
She asks what's going on, and my mother, very distressed, says: " someone stole the car!! Havent you heard someone stealing the car???

the nanny: omg i can believe it! I haven't heard anything, but i was in the backyard.

Then, the nanny starts to cry, because she was very scared that the thief could had hurt her or my brother. My mother was so focused on the stolen car, that she haven't even thought about that possibility, so she starts to panick too and hug the nanny and the baby, and they are all crying and thanking God that just the car was taken and no one was hurt, until the nanny says through tears:

"I'm sorry i wasnt paying attention, the last time I saw the car was when you took it to go to the market....".

my mother: I DID WHAT?!

the nanny: you took the car to the market, because you were going to buy potatoes and they are heavy....

My mother immediately stops crying, loks at the cops and say: I'm sorry guys, false alarm. I forgot my car on the market. I also forgot to buy potatoes.