I was thinking that I'd never been upgraded and then I remembered.....
Many years ago (I think somewhere more than 40 years ago), I was travelling from a conference in Perth, home to Sydney. I was booked with - I think - TAA.
On the flight over, they fed us only a snack in Y and I landed in Perth on a Sunday night, hungry, and nothing was open.
For the return, I was at the airport early. When I checked in, they told me the flight was delayed and they couldn't allocate seats. They took my luggage. This was my first ever flight longer than an hour or so, and I didn't understand what that meant. I did remember, however, being hungry and as the flight was now looking to stretch over 2 meal times, I went to the restaurant and ordered a proper meal. While I was eating, I was apparently called over the PA system, but I didn't hear it. I ran into a couple of friends outside when I finished and they asked me what I had done to get paged like that.
I had no idea, so wandered up to the check in desk, where they told me there were no more seats and I didn't have an allocated seat. I must have looked utterly shocked and terrified. Then they said that they might be able to fit me into First - would that be OK? I sort of mumbled "yes" and took the boarding pass. I was pretty naive so didn't really understand what that meant either.
I get on board and I'm in the last seat of the front section. My friends were immediately behind me, in the first row of Y. In F, however, they served a full meal and my friends in the next row were moaning about their snack. I did manage to eat most of the F meal.
It wasn't all fun and games though. Because the flight was so late they couldn't fly into Sydney, so we ended up in Adelaide, in some grotty hotel, for about 3 hours. My flight from Adelaide I was, sadly, back in Y