This must be on Old School mode.

Go to the back corner of Backlot past the building that looks like it is under construction.

Jump on the trash can and stand back away from the wall.

Run across the trash can and jump at the end but keep running until on the other side of the wall.

Find a black hole then jump in it.

Then run off the side and look up, you should look like you are falling down very deep.

Keep looking up and don't do anything until the map is completely off the screen.

After that press start and change teams opposite of your opponent.

You should get back to the game and you can see the other person but they can't see you.