Re: Ultron! We Would Have Words With Thee! Official Thor/Chris Hemworth Thread
From what I read, it kept falling off whilst filming fight scenes and hitting the bridge of his nose, which I imagine got really painful and annoying considering it must have been really heavy.
I think Branagh also said it didn't work, it doesn't bother me anymore, I more care that we have yet to see Thor's full power set. It's mostly just Hammer hitting and Lightning strikes.