Being a game that allows the player to do whatever they want, Garry's Mod is bound to have a bunch of these.
Trouble in Terrorist Town has its own page here.
The base game
- Placing a ragdoll into a wall or invisible physics object will cause it to flail around, making meaty thud sounds as it defies the laws of physics in the most awkward way possible. It's a staple of GMod Machinima for a reason.
- Faceposing can make characters have faces that come off as either this or Nightmare Fuel. The same thing applies to editing the bones of an NPC.
- You'll die if a prop gets flung at you too fast. This makes GMod one of the few games where you can kill an enemy using a toilet or a microwave.
- Thrusters can turn anything into a rocket that can fly into space (or at least the map border). To infinity and beyond!
- gm_flatgrass has a Mock Hollywood Sign that aptly reads "FLATTYWOOD". Bonus points for the map's hills resembling the Windows XP background.
- The description for the Rope tool:A rope is exactly as it sounds. It's a rope that connects two objects. Or you could... you know... draw swear words on the wall with it.
- The "Addict" achievement. Both its name and description qualify.You have wasted a year of your life playing GMod!
- Most of the emotes you can do via the console, especially dance and muscle.
- One of the stock props in the game is a doughnut. The textures are broken, it's ridiculously oversized, and the hole is a barely modeled black circle.
Mods
- Plenty of playermodels look extremely out of place in the game, given the ability to use realistic guns. Just imagine seeing something such as SpongeBob holding a .357 Magnum revolver.
- Most playermodel packs include reskinned NPCs, too, so you can make your favorite characters get into a gunfight. Some take it a step further, such as this Peter Griffin model, adding a buffed Combine Gunship that looks like an A-posing version of the character.
- The custom map Garry's Mall has some rather odd stores, including a Fictional Counterpart of Auntie Anne's called Uncle Gary's, a store that sells Facepunch forum ratings, and a Black Comedy store called Black Factory.
- The map also has a European Union themed café called 3A57ERN BL0C, with a rather unusual menu. Read it for yourself.
- In the map GM_BigIsland, there is a small secret area with an S-shaped modern house. One of the only things inside is a painting of René Descartes' most famous quote:Painting: Give her the dick.
- The mod NPC Voice Chat gives NPCs the ability to use custom voice lines on the same voice chat system as the players, and not only that, you can also control the pitch of the voices too, which leads to, interesting results; Usually, the enemy NPCs mainly use Team Fortress 2 voice lines for some reason. For example; imagine fighting an Antlion Guard, while it's shouting taunt lines such as "Let us wrestle, little man!" in a little squeaky voice at you. Now how scary would it be now after that?
- Most of GooBall60's "trippy" maps, such as gm_parallax. They are very bright and colorful, which contrasts greatly with the typical bloody aftermath of most GMod shenanigans.
- The Goofy Ahh Sounds pack, which replaces most of the in-game sounds with either memes or cartoon sound effects. The thruster sound effect, for example, is replaced with the opening riff of the Better Call Saul theme song.
- The Quick Fix SWEP. Based on a meme from Team Fortress 2, it allows the player to use the Sniper's rifle as a didgeridoo. The only way to stop is pulling the trigger.
- The Escape Plan, made by the same creator, is a revolver pointed towards your forehead. What makes it especially funny is that it makes the critical hit sound when used.
- There's a mod that puts the (in)famous In The Virtual End music video in GMod. There's even a chance that the vocals and instrumentals become out of sync.
- Vehicle addons such as Simfphys can include some fun vehicles to drive in, such as a drivable couch, the Patty Wagon, and Lightning McQueen.
- The NPC "dr. isaac kleiner from hl2 recklessly driving a jeep" is Exactly What It Says on the Tin. His Artificial Stupidity makes it even better.
- Two words: Rickroll Nextbot. Not only is it very much Exactly What It Says on the Tin, but it is also probably perhaps one of the only Nextbots that isn't scary at all.
- The Take the NPC is a gravity gun that chases you while spamming two of Alyx's lines from Half-Life 2: Episode One. Press E on it, and it turns into the G-Man, who greets you before exploding.
- Similar to the above mentioned base-game emotes, you can also do the TF2 taunts and Fortnite dances.
- Using the Model Manipulator on a City Scanner causes whatever model you selected to awkwardly A-pose towards you. Depending on who you ask though, this could also fall well within the Uncanny Valley.
- PAC3 allows you to customize your playermodel however you'd like. The picture alone of a female Dr. Breen is incredibly funny for someone who's played Half-Life 2.
- Parakeet's Pill Pack include various pills that are simply there to be funny. One of them is a floating Doge head with 420 health.
- On gm_mobenix_v3, there is the G-Man standing on a bridge near a bowling alley. Approaching him makes him rocket into the air and explode into bananas.
- Zeta Players, Lambda Players, and S.A.P. Bots are always random in what they say and do. The former two even accept custom voice files, so you can make them all sound like Markiplier or Luigi.
Dupes
- Someone made a melon. Made out of other melons.
- There's a recreation of the Megamind "No bitches?" meme featuring the G-Man.
- There's also a recreation of the pointing Wojak meme featuring Coach and Ellis.