The most frustrating thing would have to be the registration process. Seemingly every semester when I would attempt to register for courses, some hold was placed on my account. Interestingly these holds were never legitimate, and required me to do nothing but see the administration. By that time my ability to register for courses at desirable times was limited. Also, there were sometimes unwritten prerequisites. Courses that were recommended, and often necessary to pass the needed course were not listed as necessary.
I think the most frustrating thing about my school is the parking. Even if you try and get there early to find a spot, you may be driving around for 45 minutes to an hour trying to find a place to park.
The most fustrating thing was trying to meet with an advisor.
Nothing is really that frustrating.
I know hands down I will not be as frustrated with anything more than the initial application to this institution. There are so many new accounts you have to create, with different usernames and passwords. I am the type odd person to use the same password for everything, so it literally confuses me when I document my username and password, try to log in, and something will pop up saying "invalid username or password". I know that's what it says exactly because it's happened countless times. "How can you get something wrong when you have the answers?", I wonder in a fit of rage.