I didn't enjoy watching it. For some reason it grossed me out and I couldn't help imagining actual people dying those ways... twisted mind, I know. I wouldn't be keen on a 9yo watching it, but I'm conservative like that.
It's not aimed at kids, but at tech-savvy, viral-video-watching teenagers and twenty-somethings who are most likely to be the ones jumping on train tracks, tagging trains and trying to jump between carriages. Its a very clever safety video.
As for private parts, I told a 4yo not to show theirs to their friend in the playground yesterday. I used the phrase "We don't show our private parts to our friends at Kindy" I don't see anything wrong with the term. Perhaps it was the piranhas?