Given the information out there Gates was a jerk. A real a-hole even.

There is a very large asymmetry though between a jerk of a citizen mouthing off, and a cop using the full coercive power of the state to arrest someone for an alleged crime.

For what its worth, here's an Andrew Sullivan post of some Massachusetts attorney emails about the situation (bottom line: they don't think the officer had leg to stand in for a disorderly conduct charge).

http://andrewsullivan.theatlantic.com/the_daily_dish/2009/07/when-is-conduct-disorderly.html#more

Ditto from talking to my attorney wife about it, though she doesn't know Mass. law specifically.

A key point is when Crowley asked Gates to speak with him outside. It was moving the conversation outside that, arguably, moved it to a "public" space in which a disorderly conduct charge was possible. It's not at all clear why Crowely asked Gates to go outside if not to have a pretense to arrest him. Indeed, my wife has seen exactly that maneuver pulled several times by cops herself.

As for the veracity of policy reports, well, if we had a buck for every time she had clear evidence contradicting a police report... Not that her clients don't lie. They lie way more than the cops, certainly. But when a cop has been pissed off and overreacted, there's plenty of room to spin it when they sit down and write that report.