I feel like I could write a book about interviews
Few more things are worse than already described:
If there is no IT specialist HR expects you to know dictionary terms for all his/her questions. "What is serialisation"? The hell I know. I've used it many times, I can tell you examples right away but I have no idea how to tell you that in right way. Will Wikipedia be OK or should I memorize other resources too?
2. English language
I was once on the interview where the spoke person was very bad in English. Honestly, I can get the context of your speech if it's even in Cockney but I had real troubles to understand what I was asked about. And that was in the middle of London!
Do not give a feeling that I am not needed at all and you are in hurry. If you don't have a time to listen to my answer, don't make an appointment instead of cutting my responses after 3rd sentence.
As others stated: an IT guy is "must have" for an IT role interview. I am not going there to meet Drinking bird
or to hear "I don't know. I am here just for interview"*.
*) Happened during #2 meeting.