I debated making this comment for a few minutes... but decided (probably stupidly) to do it anyway.
What is the point of shorts that are so short ones butt hangs out the bottom? I'm not asking that sarcastically either. What is the ACTUAL point? The answer is pretty simple. Right or wrong it's to get attention and get looked at. Call me crazy but if you didn't want people staring at your butt or think it's creepy/pervy when someone does - then you wouldn't be wearing shorts with your booty hanging out? Right?
Now I'm not saying people CAN'T walk around like that. If your self esteem is so low the only way you think you're going to get attention is by having your butt hang out of your shorts - honey GO FOR IT! Do I personally think it's appropriate, oh hell no, totally agree with the OP. It's tacky and trashy. But if you wanna look a hot mess? That's your prerogative.
In equal measure it's other peoples right to have thoughts on how others dress. Because that's what the wearer of the booty shorts wanted isn't it? Attention. And oh how she got it. If only that 14 year old girl knew 'adults' all over were talking about her booty shorts. Imagine how happy she'd be.