BTW when non-native-english-speakers are asking about an idiom - we often forget to point out the obvious!
This figure of speech is a humorous twist on an earlier figure of speech ..
Fully explained here http://en.wikipedia.org/wiki/Shit_happens
Now, "shit happens" was a catchy phrase, and people standing changing it to a nice word (which was kind of cool), notably "magic happens" (I'd say that would have been a t-shirt design at first, maybe) and "kindness happens."
You then - I believe it followed in this order, but I'm not certain - people introduced this cool new use " happened", meaning, as Andrew explains, the characteristic actions (usually mayhem) that you associate with that fictional character (or real person) happened.
It would be fascinating to know the first use of this .. you can imagine it coming from, say, an action movie.
Indeed there are other variations as Bakabaka explains. Another variation is with, oh, cultural phenomenon. Oh, you might be explaining the transition in film from the new wave to pop effects movies, and you'd say something like "Everything was going along nicely with Goddard and Truffaut - and then Jaws happened."
Just as with the "Silvia" example, you tend to use it for "explosive, dramatic" things, I think.