There is an old saying "the people you meet on the way up are the same people you meet on the way down". This used to be applied mainly to stock brokers, investment bankers and other cut-throat industries, but it is as true of the insurance industry as it is of the "Wall Street" types.
It is never a good idea to trash talk anyone, but it is a particularly bad idea in an industry as small as ours. Gossiping about a colleague or bitching about a client to the wrong person is probably the fastest way to get a whole lot of people off side really quickly. You never know who knows whom, who is hiring whom and who may be "in bed" (figuratively or otherwise), so things get around pretty quickly, usually to the people you least want it to. Sometimes it is hard to resist the urge to let off some steam, but this is something best kept amongst your mates and away from industry folk.
When changing jobs, it is also a good idea to try and leave any company you work for on the best terms possible. Many of your former bosses and colleagues are likely to change jobs and you could potentially wind up working for or with them again - a situation made more awkward if you left your last job with some bad blood. If you are not leaving under the best of circumstances, always try and remain civil. Even if you don't wind up working with the same people, it is entirely possible that they will be acquainted with your new employer or colleagues - people talk and, unless it's good, you don't want it to be about you!