The classic phrase uttered in almost very
sci-fi B-movie ever made. Whether it's
earthlings landing on an alien planet, or
little green men from mars stepping out of their
flying saucer on the
White House lawn, protocol and tradition demands that these lines are said.
Once those formalities are over and done with the
slaughter can then begin.
This was parodied perfectly in Mars Attacks where the bug-eyed monsters ran amok on earth yelling out "We Come in Peace! Shoot to kill!"