The very first line of the game contains a reference to the infamous Doom Comic with the phrase "Rip and tear." Anyone who knows the batshit insanity of the comic will understand exactly what the tone of the game is about to be.
The lightheartedness of this game is at full display with pretty much everything showing the UAC's Evil, Inc. nature:
Dealing with incursions from The Legions of Hell is apparently so ingrained into UAC's operations that they have actual "DEMONIC INVASION IN PROGRESS" warnings with built in stat reports. And the "kill every enemy in the room before you're allowed to progress" sections in UAC facilities have the repeated message "Demonic presence at unsafe levels. Lockdown in effect". You know, as opposed to SAFE levels of "demonic presence"...
Then one realizes the sheer scope of how blasphemous the UAC's seven-days-a-week work ethic is: it violates the Sabbath.
"Unlike everything else in your life, the work you do here matters." "Should you find yourself caught in a level 3 demon contamination event, it is important that you remain calm. A Tier 3 Fellow wouldn't panic and neither should you."
Later on in the game, the holograms just give up entirely and speak creepy Latin/Black Speech phrases, but still in the same cheery, motivational corporate tone.
The way in which these message show how calm corporatespeak and the insane ravings of a demonic cult mesh surprisingly well together is hilarious in and of itself.
There's various signs of demonic corruption in the UAC throughout the game, but none more hilarious than the security lasers protecting the BFG-9000 being in the shape of a pentagram.
The UAC's motivation in this Doom for messing around with Hell? Exploiting it for its resources.
UAC Spokesman: Weaponizing demons, for a brighter tomorrow. UAC Spokesman: The road to Hell is paved—with Argent energy. UAC Spokesman: UAC—opening the gates of Hell with the key to the future.
Using a Munitions Crate to refill ammo will cause it to display a hologram message:
"THE UAC DISCLAIMS ALL LIABILITY AND ANY DAMAGES WHICH MAY RESULT FROM THE MISHANDLING OF MUNITIONS".
The Foundry Team Manifest encourages new recruits to get an exclusive "team tattoo" as a sign of faith in the UAC. The last line lets it slip that the "tattoo" is actually a pentagram brand!
One of the Cyber-Mancubus codex entries has a scientist state that the demon's cell is perfectly safe and secure with no way out of getting out, followed by an added [Citation Needed]. Brings to mind an incomplete Wikipedia article, doesn't it?
Once Doomguy gets his armor, he's immediately contacted via audio chat by this creepy robotic voiced doctor claiming to be the head of the facility and proposing they work together. Doomguy immediately grabs the monitor and throws it into the wall as if to say "Fuck you, I know where THIS is going" (though the loading screen implies it's more because Doomguy doesn't need help). Dr. Hayden pretty much has to But Thou Must! Doomguy into helping him.
It continues when he needs to disable focusing lenses for the argent energy to keep the foundry stable long enough to shut it down manually. When Samuel sees him break one he's immediately upset. Doomguy starts planting his foot on another one, and actually stops when Samuel asks him to, waiting for Samuel to say something that might actually convince him to listen. When Samuel pleads that the energy is unusable without the lenses, Doomguy then continues smashing it, clearly just plain done with this scenario.
At the last lens, Doomslayer clearly is trying to figure out how to permanently shut it down when Hayden pipes in that once it's destroyed, Argent Energy would disappear from the universe. One Eureka moment later Doomslayer is shoving his hand through the machine.
If you let a Revenant kill you, he'll rip off both your arms one by one, but bitch slap you with the other one before punching your lights out (a likely Shout-Out to Brutal Doom, where you can do the same to him).
Imps can perform a similar finisher; they rip off part of your armour (and tear something else out with it), before ripping off one of your arms and then delivering the finishing blow by bitch slapping you with your own disembodied hand.
Pulling off a Glory Kill on a Possessed Soldier's left leg is a capital bit of Black Comedy. Rather than tripping the foe and stomping on its head, Doomguy snaps its knee fully backwards and crushes the zombie's head with its own foot.
Dying in lava will result in the Doomguy giving the thumbs-up as he slowly sinks into meltdown. Doubles as both a Shout-Out to Terminator 2: Judgment Day and a sarcastic "well done" to the player for screwing up their jumps.
Much like in Doom 3, the presence of Chainsaws on Mars is given a Lampshade Hanging. This time however, its not due to a shipping mix-up but is described as being smuggled onto Mars as a "black market enthusiast's weapon".
Likewise, upon picking up the Chainsaw, Doom Guy shrugs before revving it up, as if he was asking himself why the weapon was here at all before deciding 'Fuck it, it's a chainsaw. It's going to kill demons.'
Even better, Olivia Pierce's name is second on the high score screen, showing that she must play this game a lot in her spare time.
Even funnier is who the top scoring player is: Donna Jackson, Id Software's office manager since 1992, under the name "IDMOM_DJ". Even when Olivia fanatically devotes herself to the game, she gets bested by someone who technically doesn't even exist.
The various collectible dolls you can find throughout the game have a number of subtly different animations for when Doomguy picks them up, all while playing a tinny version of E1M1 through the doll's speaker. But the most hilarious one is his own doll: He rotates its arm and hand in order to give it a fistbump◊, then waggles his fingers like Baymax in Big Hero 6 while pulling it back.
Getting a new weapon mod from field drones: Since he doesn't have any UAC credits to pay for the mods in questions, the Doom Marine simply punches the drone while pulling on the container to free it. The drone limply floats in place from then on, as if in shame.
Doomguy's complete lack of consideration for the deceased often drifts into Black Comedy territory, like using a body to activate a fingerprint scanner and ignoring it as it slowly slides down and falls off the console. But what about when the body he needs to progress is a long way away from the console? No problem, just snap its arm off at the elbow and carry it off.
This reaches its logical conclusion when his progress is stopped by an optical scanner. No problem for Doomguy, who simply picks up the upper torso of a dead worker, guts hanging out and all, and stuffs it in his Hyperspace Arsenal. And topping it off is the message you get for doing it.◊.
During the end credits, one of the images shows a Doomguy doll facing off against a regular-sized Pinky (which due to the difference in their sizes, looms over him like an over-sized boss). The credit info connected with that particular image? Quality Assurance.
A closer inspection shows that 'Qualtiy Assurance' is misspelt.
Most of Doomguy's characterization becomes this when you analyze his mannerisms; basically, aside from killing Demons, this guy does not give a single flaming fuck about anything. Someone dumping exposition on you through a computer teminal? Shove the terminal away. Someone trying to justify their atrocities to you? Smash the comm-pad. Someone begging you not to destroy a vital piece of equipment for the sake of progression?Destroy it faster! The Doomguy's storeroom of fucks to give has run empty long ago, and he is not going to the store anytime in the foreseeable future.
SnapMap's descriptions for items and features are surprisingly full of gems. Here's a small handful to start:
You can choose whether or not there should be clutter on the floor, walls or ceiling of a room module. While the description for Floor and Ceiling clutter is straightforward, Wall Clutter states, "Hey, my Pink Floyd poster is NOT clutter!"
For unused doors, you can select a variety of door caps. One cap features a couple of terminals - apparently the one on the right has DOOM2.EXE on it. Another cap features a wall of screens, its description stating that every professional computer user has at least five monitors.
Even the Modules themselves have funny little descriptions. From jog pieces being used to connect areas 'separated laterally by seismic activity or bad planning', to connector pieces being used to correct pesky rounding errors in Martian architecture, to Repair Bay 9, which comes with an 'optional equipment fire'.
The Hell update for SnapMap has some more humorous descriptions for it's new content. One such description for the Red Skull Key says that if you 'put your ear against it, you can hear the distant sound of trumpets.' One has to wonder if that's a reference to the somewhat infamous Doot◊ meme.
After getting the BFG-9000 and falling into the pit, the first thing the Doomguy does is immediately check to see if he still has it.
When the structure holding the BFG collapses, he immediately holds it against his body protectively.
Playing the classic Doom levels uses the classic levels and textures, but leaves the model designs alone, with one exception: your helmet◊ will show the classic face of the doomguy if you die.
The cutscene that introduces you to your first Imp becomes Hilarious in Hindsight when you later learn that the Doomguy is The Dreaded to demonkind. The poor thing probably wasn't roaring to intimidate you, it was likely scared shitless!
Pretty much all of the taunts count as well, especially the Humor and Mock ones. They're so out of place in this otherwise dead serious game it's hilarious.
The various scenes where you encounter demons infighting, such as a Baron of Hell going ham on lesser demons, Imps using Unwilling as target practice, a Revenant fighting a Mancubus for control of a tiny floating island, and a group of demons guarding The Crucible who suddenly turn on each other as the Doom Slayer approaches.
A more subtle one, but in the level where you meet Samuel Hayden face to face, he gives you a bit of exposition, and then ends with "the service elevator is at the end of the hall" while making a dismissive motion with his hand. Sam Hayden low-key tells Doomguy to get the hell out of his office.
Pretty close to the beginning, the Doom Slayer walks into a room filled with blood, gore, and all the other stuff one would expect in a demonic invasion. An automated voice announces, "Welcome to the UAC! Now 221 days accident free!" Apparently everything literally going to Hell isn't considered an "accident."
The Slayer Testament says that "The mark of the Doom Slayer was burned upon his crypt", but nothing other than the mark on his helmet suggests that the Doom Marine personally made it his mark. He even wipes at the mark when he sees his helmet, meaning either he was just getting some dust off it, or he was trying to get some weird red scratch off the helmet he hadn't seen for however long he was cooped up in the sarcophagus. "What the heck is... ah screw it, I've got better things to think about." *puts on helmet*
Thanks to the Update making the Praetor Armor available to multiplayer, you can put it on, put the appropriate colors, and... Make him do all the emotes, want Doom Guy to do the aforementioned Doom Shuffle? Well now you can!
A popular fan theory holds that the first imp you encounter in the game isn't roaring to intimidate you, it's screaming in sheer terror upon realizing that Doomguy is awake again.
As well as the "He is here!"' line you hear at the beginning of the Hell section. Which can be interpreted as a sign that Hell is collectively crapping its pants at the Doomguy's arrival.