Not a car, although I have done many stupid things in them as well, but the most embarasing was on my 25 year old Honda CX 500 custom bike.

Cooly walk up to it, as it leans on it's kickstand, shining in the sunlight. Don the shades and helmet in view of onlookers on a busy street. Smile with satisfaction as it fires first time with a throaty roar. Casualy backheel the stand out of the way, pull the clutch, snick it into first. Look round, nothing coming. Set off smartly and then fall off as you realise that you have not taken the front disklock off...

Glad I can laugh, although it hurt more than my pride!

:D (eG)