I don't think you can open the door on a 777 in flight.

For comparison the plane that D B Cooper used had a stairway in the back(sometimes called airstairs). He was able to override the in flight lock and get out that way. My understanding is that the db cooper incident is in a large part why they don't put airstairs on planes any more.

But now you have me watching videos on 777 doors. they open outward than forwards, like most airline doors they probably have a interlock to prevent them from opening in flight, if you could override that, I don't think you could push them forwards against the slipstream.