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 depends on the way that the DDOS is implemented. If it's simply an executable distributed to multiple machines, making simple HTTP queries using native TCP sockets, then Google Analytics wouldn't notice anything at all: because the JavaScript that gets returned would never be executed.

However, other sorts of DDOS attacks could leverage actual browsers distributed across many machines. For instance, if you could hack the Yahoo home page and insert an `<iframe src='takemedown.com'>` into it, you could easily DDOS "takemedown.com". In this particular scenario, GA would certainly detect the impressions, and because (depending on the scenario) there might be an HTTP referrer tag, you could possibly run a report in GA that could pull out the suspicious impressions.

But there are other similar scenarios that wouldn't leave any particular footprints. For instance, if you could hack Lady Gaga's twitter account, you could send out a link to her 16MM followers, and a significant number would immediately click on it: and since most of those clicking on it would probably be doing so from within a separate app, there wouldn't be any referrer tag, and no particular way of identifying the requests.

In other words, it all depends, but it's probably not a terribly useful avenue to investigate. In many (most?) scenarios, GA wouldn't even recognize the impression; and in many others, wouldn't have any reasonable way of picking out the good impressions from the bad.