There's a difference between mobile numbers and number plates. People can't use your number plates to contact you.
The way I see it, people can say what they like. It's a free country. If you don't want people commenting on your behaviour then do it where no one can see you. There's nothing wrong with giving your opinion on what you see. Bear in mind that the roads are public property, they belong to everyone, not to mention that the behaviour of Skyline drivers (and other imports) reflects on other Skyline drivers. So someone may think it's ok to drive like a tool, but it might be me getting pulled over next week to be checked for defects.
As far as giving out number plates is concerned, I'm pretty sure (and would appreciate confirmation from someone who knows for sure) that a forum post has no legal standing as evidence. I can say, "I saw charli doing this", and even if a cop reads it there is no way it can be used in court. I would have to provide some sort of witness statement, and even that would have to be backed up by some sort of evidence. You can't get busted just on someone's say-so, unless that someone is a cop. That's my understanding anyway.
And if you have custom plates, you can't expect to be anonymous. People are going to see and remember, and isn't that the point? Custom plates are supposed to identify you. If you have normal plates then it's different, but if you've got custom plates you can't pick and choose when people notice you and when they don't.