I work in the IT department of a bigger company.
For the last couple of months I have been in charge of tech support of a couple web applications, I only do this occasionally since I work in software development full time.
A specific person, the head of a different department, is well known for somehow always experiencing issues with his software or computer equipment in general, but mostly the issues appear to be because of his own wrongdoing.
This person is also a user of said web applications. Since I'm responsible for them, he takes every chance he gets to ask for my presence so he can explain to me everything that "is wrong" with them, complaining about how he has to waste several hours each month (web apps are used on a monthly basis) to try and make them work but still they don't. He gets aggressive enough to complain loudly about how we may have time to waste but he doesn't, about how it's unbelievable that he has to every month call someone and show them what's wrong and still nothing gets fixed, about how he thinks we are doing it on purpose so he can't take care of whatever else he's supposed to do, about how can we develop such horrible systems that nothing ever works on them. Basically he thinks it's garbage, and he knows I'm the only person responsible for it so the use of "we" is only a euphemism.
Now, in a way, I understand some of the things he says, there are several things I see on the software that I probably would have done differently, but that's the issue, I didn't develop it, I didn't design it, I wasn't even an employee before this was up and running. And it's not like I can just say I'm gonna work on that because he keeps complaining, I'm part of other projects, with several deadlines that take all my work time and even more in many cases.
However I don't tell him that, I only tell him the truth, every time he calls me I try to explain the same things, that some functionality is actually designed to behave in such a way (it is), that there are things that because of security he cannot do, that the software works as it was intended to and so on. But it serves no purpose, he just keeps yelling at me because "well... but it doesn't do this and it doesn't do that... and also...".
My direct boss is aware of him and the so called issues he complains about, then I'm told I probably shouldn't worry too much about it.
But still I'm the one that has to keep getting yelled at because of others' past decisions plus the lack of greater understanding of this person. He's even passively aggressively threatened me to talk with the head of my department and complain about how everything "we" do is garbage. Something I'd have no problem with because he also uses those web apps and doesn't experience those issues.
I like my line of work, I enjoy it, I strive to make the best out of everything I make. And it angers me that basically he tells me I am everything I try not to be. I have no idea if he does the same to other people, he might as well, but I know for sure he didn't do it to whoever was responsible for this before me.
So, if you've read all this through, how could I deal with this?