As an Austrian, it would not make much sense for me to participate.
However, it would be * technically * legal to only wear loincloths in public here, as only total nudity (and sexual intercourse) is prohibited in public. You have to cover your genitals so that you hide them in any situation, but that's what loincloths are about, isn't it? However, there is the rule of dressing appropriately. If the police believe that your clothes are disturbing public order, you can be fined. It's not a criminal offense, it's a petty one. You can also be denied access to shops or public transport by the owner or his agent.
The issue I have with this is the people who would walk around naked are the people who shouldn't be walking around naked.
They're the same ones who frequent the beach in thongs and speedos. Just because spandex stretches doesn't mean it should.
Not to mention the huge can of worms it would open which I won't delve into.
I think the petition should be at the very least an expression to wear whatever freely. Providing sexual organs are covered up. So loincloths obviously would be acceptable. And at the most... topless women.
Given I've seen more guys with bigger **** than porn stars shirtless, it really shouldn't be so taboo.
