Question: What i'm wondering is, what kind of behaviour does google analytics show when a ddos attack occurs? Any theories?

Answer: 
My theory would be that an effective DDoS platform/script would *not* include anything as heavyweight as a JavaScript engine, and that therefore the DDoS activity would not show up in Google Analytics at all. 

The point of a DDoS attack is to overwhelm the server with a flood of requests. Any CPU cycles that are spent evaluating JavaScript in the response that the server sends back are cycles that could better be used churning out more requests to the server. I would fully expect a properly executed DDoS attack to not waste time parsing the response from the server, or even reading it off of the underlying socket, let alone interpreting and executing and JavaScript that may be embedded in the markup or fetching scripts and other resources from domains other than the target server. 

Of course, this does not preclude the possibility of an exceptionally naive DDoS attack implemented using web frameworks and libraries that *do* evaluate embedded JavaScript. Such an attack would not (or rather, *should not* if you've implemented your server code correctly) be very effective, but it would likely generate a spike in Google Analytics traffic.
It will show up 100% some significant peaks in google analytics , simply because there are huge number of requests from multiple sources having huge bounce rate !