DXpeditions are put on by people that wants to put a rare entity on the air. They are usually self sponsored, followed by sponsorship from local clubs, regional clubs, national clubs and also personal donations.
Their goal is to put as many call signs in their log books as humanly possible.
These DXpeditions are advertised at least one year in advance and their call signs are listed by both the ARRL and QRZ.com
If you are too dumb or too lazy to know how to look them up, and all you do is hear something or see something on a spotting network and decide that you want to crank up your amplifier, twist your beam antenna their way and try to work them, more times than not you won't be able to, at least not on the first try!
The contesters that travels to these places do not use their own voice, but a voice guide or a program such as N1MM that allows them to record their exchange and all they do is push a button and give out numbers and verify call signs. OK
Usually if you have people from the USA that are unruley and acting like jerks, they have a 5 in their call sign. It seems that the people from Texas that came from the CB radio, that believes that everything is bigger and better in Texas are the main trouble makers. Georgia and Alabama comes in a close second.
Anyone that has ever dealt with Todd Burnett and his wife Chandra will attest to that one!
The best thing you can do is to follow the DX University rule for contesting and spread out and hope that they will tune to your frequency.
Here is the basic principals that they teach at the Dayton Hamvention DX University.