Like Punki, I don't think I've ever screamed, but I have once let an agent know that they are going to do something for me.

Flying from SEA back to BOS on UA when I was in college, there was a huge snowstorm on the East Coast. My BOS flight was canceled when I landed in ORD to make a connection. The lines up to the service agents were insane, but I got to the front, handed over my now-useless BOS boarding card, and heard "We booked you on the next flight tomorrow morning." I had been looking around at the nearby gates while in line, and a flight to EWR was boarding right across the hallway. I told the gate agent I wanted to be put on the EWR flight, where I would spend the night (with family) and then I wanted to be put on a EWR-BOS shuttle for the next day. The agent told me it was impossible, and I asked by how many seats the EWR flight was oversold. She looked at me, I repeated the question, and she printed up a EWR boarding pass for me. I made her also give me a seat (not just a reservation) on the BOS shuttle from EWR the next day, then ran over & was about the last person on the flight.

This was one of my first solo transcons, and to this day I don't know how I had the nerve to do that- I just was not about to spend the night in ORD sleeping at a gate.