I was 16 and my mum was away for the weekend so the boyrfriend and I were making use of the opportunity. The foot of my bed pointed towards the bedroom door.
A family friend who had a key let himself into the house and called "Anyone home?!" - we kept quiet, but I never told my boyfriend that over his shoulder I had seen the family friend silently open the bedroom door, see us
and just as silently back out and shut the door ....