Look at it this way: Parker knew it was bad. He knew people would be laughing at him. He did it anyway. Why? Because to him it was a way to get a laugh. He was having a lot of fun; his team had just won the NBA title. Just like when Tag put on the RCD shorts and did the little dance. He wasn't embarrassed because he did it to get a laugh. Now if the shorts had split, that might have been embarrassing but considering Tag, I doubt it.
The same holds true, I think, for Tony Parker. I think he made a conscious decision to make a fool of himself to show that he could let loose and have fun just like everyone else.