A predator mission given to you by the south-central garrison: Fight and kill four mutant turtles in the sewers. First of all, it turns out they're just glowing Galapagos turtles...and second of all, these turtles really are ninjas, laying booby traps for you!
Also, each of them has a different colored stripe around their eyes.
Numerous little things, such as the descriptions for missions:
Omega force is investigating nearby ruins with a scientist in tow.Let's call him Susan. Mission: Desperately Saving Susan
The Rejection of the Unknown Drug Darling tries to give Rex.
Rex: Sorry Doc, I swore an Oath to a Special Lady?
Many of Rex's punny One Liners are likely to inspire a chuckle, but the funniest instance of him using one has to be in a conversation during a mission when an assisting scientist catches him using the same quip twice in succession.
Oh yeah, another one down... What the fuck am I doing?
10 million dollars to bring me back and I am doing this?
Instead of inserting shotgun shells into his shotgun, Rex tosses them in like coins.
The fact that the tutorial is so snarky and Rex himself is aware of it and raging about not getting to kill things.
An extra layer is that Spider deliberately activated the tutorial just to piss off Rex.
Rex: "Oh, you fucking asshole."
The VHS Tapes you collect are hilarious in their own right, as they parody films of the 80s in all their cheesy glory. These include a buddy cop film (and its mandatory sequel) called Boiled Egg, which is a pun based on the protagonist's name; a Revenge of the Nerds homage called Popularity Camp; and Even Score, a film described as having every action film cliché imaginable, including German terrorists, defusing a nuclear bomb and a kidnapped US President, all of which takes place in a football stadium, of course. One of the more hilarious ones is called Hard Labour - The Seduction of Dale Pretty. The description pretty much spells out that it's a movie about prison rape without ever actually using those words. The innuendo for the film is darkly humourous, the final quote claiming that the film is "a damning indictment of the American Penile System."
When ever Rex completes a mission, he throws up the horns as if he's a rockstar. Not just any horns, though - they're horns with electricity arcing between the outstretched fingers.
What does Rex do when you press the melee button with no one in range? Give the middle finger. If you press it repeatedly in rapid succession, he'll alternate hands.
The basic first aid animations (for when you're out of medicine) include Rex pulling a welding torch from nowhere to use on his cybernetic arm, reconnecting a wire to stop his hand flopping around like an octopus, and...squeezing a perfectly mundane hand-spring with his normal hand. Really fast.
In one of the missions:
HUD: Objective: Punch the nuclear reactor.
The description for some of the weapon upgrades, like laser rounds for the Fazertron.
Because science both rocks and burns at the same time.
The description when you get your first Predator mission says that you're pretty much just going on this mission "to prove that you're King Shit."