The other day at work I was strolling along the top-floor corridor towards the Gents', texting my other half as I went. When I arrived at the urinal, I found my flies already undone.
It's possible, of course, that I hadn't zipped up again after a previous visit. That would be embarrassing, but only mildly so. We all do it occasionally, after all.
What bothers me far more is the possibility that whilst wandering along the corridor past colleagues of varying seniority, contentrating on pressing buttons on my phone but subliminally aware that I was heading for the lavatory, I might have absent-mindedly unzipped as I walked, to save time later.