Ok well this happened a few weeks back, I was initially mortified by the incident but after getting over the embarrassment I quite naturally thought to myself: eureka! just the type of thing to post about in AH!
So I'm walking along a city street, sunny day, early afternoonish, on my way to run some errands, quite pleased with the world in general and with myself in particular, carrying my trusted big aul rain poncho (if you know anything about Galway weather, you know why) slung over my arm.
When all of a sudden, there's a toot to my right in the road, and a van has stopped beside me and the man in the passenger seat is addressing me for some reason. Possibly asking for directions? So I saunter over in a helpful manner, all ready to issue directions etc. But no. What the man actually says, very mannerly and very casually, is this: "excuse me, er, but your skirt was lifted up. By your coat, I think" or something in a very similar vein.
The rain poncho I carry with me has a lot of loops and hooks on it. One strappy thingy had caught on my skirt in the general area of my behind and had lifted it all the way up. All the way. Thank god for the cold of the winter time and my trusty big aul 90 den black tights! - although it was probably that extra layer that stopped me having to feel some extra cold on me arse and copping on to what had happened.
Now, I am extraordinarily mortified. I could probably pass for Mrs Tomatohead. While immediately attending to my uncovered arse, I simultaneously thank the man in the van profusely for alerting me to the ongoing disaster and am in my head already counting how many people have possibly seen the spectacle since I left home or thereabouts.
The men in the van, though , thank you.

True gents. Off they went then.
What happens next, while I'm still standing there, just struggling to mentally readjust to my sudden fall from grace and loss of dignity, and helping myself in the endeavour by repeatedly smoothing the skirt over my bum, is: a youngish fella passes me from behind (of course), with a huge grin on his face and an enthusiastic and animated wave of both his hands in the manner of "best thing ever!!" And exclaiming excitedly to me: "I saw that!" Yes, thank you, young man. Wholly appropriate and infinitely helpful, many, many thanks for that. ( well, at least he didn't say "I saw YOUR ARSE - in truth, what a whopper!" or "I saw that - great craic!" - so thank heaven for small mercies etc.)
Ah the men of Galway... They're the best

I carry my rain poncho strictly scrunched up in a ball, or safely tucked away in a plastic bag these days.