It happened to me once, this past christmas.
I was waiting downtown for the bus to come, when suddenly a complete stranger came up to me from behind and asked if he could have a listen to my HD25-1. I was, naturally, a little surprised and need a few seconds to understand what was happening.
I finally answered 'yea, sure, no problem'. As it was freezing cold (-15°C, late in the evening), I had a lot of clothes on, so getting the headphones of, wire and all, was a bit of a struggle, but finally I managed to hand him the headphones. I asked 'so, do you have a player to test 'em with?' He didn't, so I fished out my iPod too.
I had recently been listening to some Drudkh, so I asked him wether that seemed OK to test with, explaining that it was pretty straight Black Metal. 'fine' he said, 'but a track with some prominent drums would be appreciated'. I started the track, and he started listening. A bit of chit-chat followed. He had been wondering about the 25's for a while and just couldn't let this opportunity get past. He said he liked the phones, and that the drums sounded quite tight and impactful. I agreed and said I considered this to be among the headphone's strong suits.
He thanked for the listen, I said 'no worry', he went back to his business and I continued waiting for the bus.
So, would I have done the same in his shoes? Doubtful, but at least now I know tat it's possible. And it was a rather nice experience actually. A bit strange and awkward, but nice.