Have to admit, I know buggger all about wing flexing, so I'm not in a position to answer phase slag's question.
While all answers here are interesting, and I'm sure that they are technically accurate, maybe the subject could do with a bit more sensitivity? Phase slag describes himself as "not the best passenger in the world", and I don't think stories about how the dean of an engineering school wouldn't sit near the window of a 727 are going to do much to make his travelling experience more pleasant.
Phase slag, it seems that the message from this thread is that the wings would have to bend an extraordinary amount before there's any danger of them breaking. In fact, the flexing is actually beneficial, as bendy objects are less likely to snap.
Personally, I think flying is one of the most amazing experiences, and the view from up there can't be beaten. Try to relax, enjoy the view, and don't let the wing flexing worry you!
FFF
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