The reason this easter egg is useless is because it was made for me and my friends. I salute you if you try to do this for no reason other to feel accomplished.

STEP 1:
Notice the sign that says "HAVE YOU SEEN THESE?" near the second staircase.
You have to shoot all these (with a pistol or rifle, no lasers or explosions) in order from left to right. Shooting any of these out of order will restart it all.

1 - in spawn room on the cart
2 - under the bench in the second room after spawn (near first monster can)
3 - behind muscle milk perk machine
4 - inside the vent near where you build power (must do the fund applebees EE)
5 - wunderfizz room with raygun wallbuy (must get the keycard from monster can EE)
6 - behind bull ice blast (again, must do the fund applebees EE to open the vents)
7 - over the train tracks in the staminup room on the wall
8 - inside the bathroom sink in applebees (yes, it exists)

STEP 2:
Grenade the shark in the spawn room. it's sitting on a chair outside the map.

STEP 3:
Eat the tomato in the applebees kitchen. Use the toilet found by buying the Gold Edition smelly subway.

STEP 4:
Find the fire extinguisher inside the room with the "Harris" shootable (near electric cherry).

You must put out the fire on the computer inside the computer room (near widows wine). This will lock you inside the room for 1 min, feel free to cheese it.

When you pick up the computer, deliver it to the person ontop of the cart in spawn.

STEP 5:
Collect all the cube friends around the map. Any order.

1 - blue wallpaper room behind washing machines
2 - in the room where the fire extinguisher was at (electric cherry)
3 - on the shelf inside the room near tombstone
4 - inside the wunderfizz room in applebees (in the restrooms)

Deliver the cubes to the person in the room of who's who.

STEP 6:
A train has arrived near staminup room. Interacting with the train will start a timer for 1 minute.

You must run to the applebees kitchen, find the burger carton (does not spawn until you start the timer), and run all the way back to the train in time.

REWARD:
The truck and crates between spawn room and applebees will move out the way, enjoy.