/ basically means "aggressive" _in a positive sense_. It's an antonym of "modest" or "conservative".
What is considered largely depends on the context. If someone's outfit is relatively more eye-catching or fashionable than usual, that alone can be a reason one would say . An otaku might be told "!" just by dressing like a normal person. And it can be closer to "outrageous" if used sarcastically and euphemistically. Try an image search for , and you'll find a lot of people dressed in extraordinary ways.