Sure, you might argue that anyone who tries to work under a car which is only held up using a jack is making an Darwin Award-style contribution to improving the gene pool. That said, 46 people in Australia have been killed over the last 10 years doing just that, which has led to the ACCC launching a campaign to remind home mechanics not to take risks when fixing their car.
The campaign covers basic advice -- use support stands and a trolley jack to work under a car and make sure that there's no-one in the vehicle when you raise it -- and also points out the safety standards which jacks and stands must meet to be sold locally. Hit the link for all that information, and share any additional mechanic safety tips in the comments.
Don't be a jackass with jacks [Product Safety Australia]