The interesting thing to keep in mind is that your users are often operating under deadlines. Deadlines they could have made if the liberal policies currently in effect were not in effect, and as such, you are seen as an impediment.
It's short sightedness on their part, probably coupled with poor planning on either their or a superior's part, but the stress they feel is still there, and it usually manifests itself in said rudeness, skirting of said polices, etc.
For example, our IT department decided to implement a much more comprehensive firewall than before. It had the unintended side effect of blocking eclipse plugin downloads (which apparently usually operate with an SSL certificate, which is currently being hijacked by our organization's "security solution", and so refuses to work).
I could either a: wait the 3 days (made even worse by not knowing, at the time, it would take 3 days or 3 months) and do zero work, costing my project a few hundred / low thousands of dollars in lost labor in the process, or b: figure out how to get around it. Being a nerd yourself, which would you submit to? Especially if you have a deliverable 5 days out, and you don't really fancy the idea of working 18 hour days just to make up for the lost 3 days in the short term?
As soon as I had access to the tools I needed, when I truly needed them, I stopped skirting the system. I'm not there to be a jerk and I'm not trying to make IT's job miserable. But I am (I hope understandably) irritated when IT institutes something new like this, without fully testing it with a pilot program, without noting the majority of these gaps in expected service in advance, and without notifying any of the programs operating within the official infrastructure in advance (some of our programs have their own segregated intranets for their development, and so don't really have this problem - mostly because they have zero connectivity to anything outside themselves).
So keep in mind - what seems to be a perfectly reasonable policy to you (and, in fact, it is), is going to cause some people some (in their mind) unnecessary stress as they try to meet their own deadlines. This doesn't give them the right to be an ass to you, but it may help if you put their behavior in context. The subtleties between being genuinely stressed and upset and being a rude jerk for the sake of being a rude jerk are sometimes lost.