Free upgrade
I did it once but by pure chance. I was boarding an AA flight to POS and my client was in first. I stopped to chat with him and sat down to keep out of the aisle.
CC came by and offered us both a drink, which I took. Amazingly I seemed to have plonked in the only empty seat in first class. By the time boarding was finished I just stayed put and enjoyed the meal and the booze.
First time I ever flew in fist as well.
Sometimes you just get lucky.
20driver