Let's start with the opposite. One way you cannot get an upgrade when you're flying is by schmoozing with the flight attendant. They simply don't have the power to do so. Almost all of them will tell you that they'd be risking their jobs if anyone notices them giving you preferential treatment over the other passengers in economy. One possible exception – if you happen to be in the armed services and are flying in uniform.

Now if the economy class is overbooked and there's space in first class, the gate people may be able to give you that upgrade – with much more difficulty now than ever before. It's tough because usually the airline's elite fliers will have first dibs at an upgrade. This means the first class cabin would usually be full before you even get to the airport.

If you're stuck in the airport because of weather delays, one thing you can do is to try to be friendly and nice to the gate personnel. Most other passengers are already upset that they have to sit another two to four hours at the terminal before they can fly, so a nice friendly passenger like you will definitely be a welcome change for the gate agent. If they have the space, they just might give you that last first class seat for free!