Mine happened 18 years ago, and is actually an "On the way to WDW" moment.
We boarded the plane for the flight from Philadelphia to Orlando and found that our two daughters, ages 10 and 8, would be sitting in the row in front of us. We waited anxiously to see who would be the lucky person who would sit in the third seat with them, and were a bit dismayed when a very businesslike middle-aged gentlemen took the seat. My husband and I just prayed that the man, as well as the two little girls, would have a smooth flight. Over the course of the flight, we heard bits of conversation from the seat in front of us, but we really had no idea what was going on up there. Finally, we landed in Orlando, and our daughters' flight companion unbuckled his seat belt, stood up, turned to my husband and I and asked, "These are your two daughters?" Not knowing what might be coming next, we told him they were, indeed, ours. He said, "I have to tell you that when I first boarded and saw two little girls in my row, I thought I was in for one heck of a flight, but I found them to be very well behaved and interesting to talk to. You should be proud." We were immensely relieved and so grateful...both to the girls for making us so proud, and to the man for taking the time to tell what he thought of his traveling companions. What a great start to a great vacation!