Well I have to agree with aerlik, there are plenty of backstabbers in aviation, I suspect however they are in all similarly competitive industry (just watch The Apprentice some time!).
Rather than turn this on aerlik (good on him i say - if you're not happy, cut your losses n get out) I'm gonna add a couple of experiences I've had over my GA years.
In my very first job the CP took a disliking to me because I asked for a retainer for all my office duties. He then asked me to go n get my IR, which whilst I was doing, proceeded to tell the owner I'd up n left without notice, resulting in my job being taken. Nice.
Later I had a casual pilot go telling complete lies to the owner in an attempt to get me fired so he could take my full time gig. Luckily it didnt work but it came mighty close.
Then there was the guy who let slip one day that he "didnt care who he had to step on to get into an airline".
Finally I had another pilot tell more lies about me in an attempt to get me fired for personal reasons, which basically forced me into a position where I had to quit.
Having said all this the majority of the ppl I've worked with have been top blokes/ chicks and are still my friends.