The word-dude is almost used everywhere, esp among young people. Of course, it only refers to man. Girls do not use it that often though. It's just a general slang.

freak out is a really widely- used word. It probably does not have a corresponding word in Chinese. Its use is very general and not well-defined either. You can use it to describe any reaction one person may have under unusual conditions. I even heard it used on objects instead of people.