Wooooooow!!!
I don't know why I didn't bring this particular topic up before myself because it's one of the most arousing things I can ever think of.
I love these "accidents" as a very big "oops moments" fan, but they also amaze me as a BE lover too, because they're the most basic side effect of not having total control over your big boobs.
Of course, the situation adds a lot to the whole moment. It's pretty much usual to see partial areolae in porn and I still love that, but I can get all crazy over a candid pic/video or a TV cap specially when the gal in question doesn't know what's going on... or she's even trying hard to cover them, but she can't.
Just another sample... I'll try to look for more.