Previously I had Hanes cotton briefs (the same style) in a size 10 and they fit fine.  These, however, were tight.  I took them off and measured them against an unworn pair from my last set of Hanes cotton briefs, which were purchased locally a few years ago.  Those were two inches bigger in the waistband than the ones I just bought from Amazon.  It seems likely Hanes has changed their sizing.

Clearly this is a manufacturing issue, not a vendor issue.  It's not worthwhile returning them -- I'll just pass them along to someone who's a smaller size.