Play the "Desperately Saving Susan" Nerd Rescue and go to coordinates X: 479.1, Y: 488.3 to find a Xenomorph egg from Alien behind the nerd you are saving. Note: Michael Biehn, who voices the main character, was also a cast member in Aliens.
Dungeons & Dragons Reference
When you need to distract an enemy, you can throw a twenty sided dice at them.
Far Cry 3 Reference
Swim underwater at coordinates X: 531.2, Y: 321.5 to find a scientist next to a toilet, similar to the seasick soldier found in Far Cry 3.
You can give people the middle finger if you hold [Melee]. You can also press it multiple times to use both hands.
Teenage Mutant Ninja Turtles Reference
During one of the Predator missions, Rex must kill four turtles in the sewers. You can find a pizza box in the sewers and each of the turtles are wearing colored ninja masks.