First ever car Mk3 Cortina and around 6 years old when bought.
I thought it was a good idea to fit an after market oil pressure gauge. After fitting, the gauge took about 30 seconds to register so I concluded that I had a problem with oil pressure.
Removed the gauge adapter and asked a friend to start the car while I checked under the bonnet. As the car started the contents of the sump shot out of the hole in the adapter, missed my ear by a few inches, hit the underside bonnet and descended again covering everything within a 3 foot radius.