I'm Confused

Alright, something has been bugging me a lot. I heard that yesterday, some girl with an innertube won the dress up day contest. I'm pretty sure that no one would be allowed to do that on a normal day. I know, it's because it's Sadie's Week, and that weird stuff is allowed. Fine. So how come last week, on the national no shoes day, people got in trouble for not having shoes? Sadie's Week is an event for fun at our school only, while the no shoes day was a country-wide event to raise awareness for a good cause. Both required clothing that normally wouldn't be acceptable. So how come we were allowed to do one but not the other? I'm not saying to get rid of Sadie's week, just to allow us to express ourselves freely. I'm stumped here, can anyone help me figure this one out please? Thanks.