I’m assuming this was on a BA flight as it was about 30+ years ago. I was working in Paris at the time and had come back to London for the company Christmas do. I was scheduled to fly from LCY to CDG on a Monday morning. The plane was a turbo prop and there were only 4 passengers. Some bubbles were offered pre departure and then some more in the air. As I was the only one drinking at that time (I was in my 20s at the time) I was invited to finish the bottle. That resulted in some Dutch courage so I asked the flight attendant if I could sit up front for a little while (was learning to fly at the time). They had a quick word with the captain and they gave me the OK. I got to sit in the jump seat for a little while and had the flight of my life.
Not possible these days.