While being an intern I had to make a finance system, no requirements except for the fact that it has to invoice the right person...

As soon as it was seemingly done, I'd go to the customer and he'd just say "why isn't x in there? This isn't what I meant! Where is y feature? Why does it work like this and not like that?" etc...

I had 0 experience, and was just told to make stuff as I went, horrible experience and truly the most frustrating project I've ever done.