Some good stories here. Allow me to add my own.
About 10 years ago, a good friend and his fiancee asked me if I'd marry them. I was flattered, but I am not a priest nor do I have the ability to perform a legal wedding ceremony. What on earth was going on?
Well, his fiance had just become pregnant and it turns out that they had married in secret a year or two earlier. They didn't want to break the news to their families that they had married in secret, in order to avoid upsetting anyone. They did, however, want their families to know that they were starting their own family as a legally married couple. The plan was that I would dress up as a priest and marry them in a ceremony that their families and friends would attend so that when the bride gave birth, everyone would think they were married - which they were (just not by me).
The "marriage" ceremony and reception both took place on a large ship docked at harbor. The groom rented a set of priests clothing for me from a costume store. We figured out a ceremony between us, and I gave a sermon. Heaven knows how I pulled it off. Luckily, neither of the families had met me before, but I had met the groom's best friend briefly once, and he seemed to remember. After the ceremony, he asked me what denomination I was. I replied that I was non-denominational - that the church I belonged to was ecumenical and open to all. He gave me a long knowing smile in return and at that moment, I knew he'd figured it out. Then the groom's mother came up to me, touched my arm and said, "Oh Father, that was such a wonderful and inspirational sermon. I feel so much closer to God." Wow, did I feel guilty!
A couple of years later, I ran into the best friend again and we talked. He had indeed figured out what was going on. I heard from my friend who I married, that they later told their families, who took it very well. Apparently they understood the intention, and saw the funny side. Thank goodness for that. There are some people who would be very upset at such a ruse but luckily, this particular group of people are a very accepting and loving set of folk.
I still have the picture of myself dressed up as a priest, with the couple. To anyone who knows me, the thought of me as a priest is a bit far-fetched. I did play the role of Jesus in nativity plays at school every single year, so there must have been something about me that seemed pious. I'm still trying to figure out what it is