Thanks for all the... err... Interesting responses guys...
It's as simple as this. I opened my house, went inside, got my stuff to clean my car, opened my boot to get my tool box out, shut the boot and washed my car. THEN realised the keys were in the boot, and I must have pressed the lock button as I opened the boot, or something.
The car was bought second hand, and I DO have a spare key, however, I leave that with a mate who lives near where I work, that way, if I DO lock myself out of my car, he's never too far away from me so he can bring the key around.
That mate, the EXACT mate who has my spare key, was playing a gig at the Espy in St. Kilda, and I had to go watch him play. So you see my dilemma.
Luckily, he had left the spare key at home and his mum was kind enough to arrange for it to be dropped off to my house.
How good are your mates mums ehhh!?