Sorry to hear of all your bad experiences lads.
I have to say, between the Unit and EKPark, both of which I've only been to a few times, and Kelvingrove, which is my local, I don't see much of this happening.
There's always been a healthy level of respect shown between all the riders and skaters, especially at KG which has a great atmosphere. This may be due to the large number of older riders and skaters that have been going there for years.
I know that I certainly don't tolerate any bad behaviour at KG. (Especially bullying - I f@kin' hate bullies).
Sure, there's always some kids getting in the way, but you know that's because they don't know any better, rather than them being deliberately obstructive. I find that a bit of 'skatepark etiquette' instruction usually does the trick.
Saying that, I know exactly the kind of little pr1cks that seem to think they are untouchable and make everyone else's life's a misery. As has been mentioned, riding at them at high speed and giving them a few near misses usually does the trick.
If that doesn't work, don't miss.
G