Slapstick Requires Simulation
I've been playing Skin Deep lately, a really good and funny immersive sim by Blendo Games. It's funny in many ways, the writing and overall conceit are both very goofy and taken very seriously.
I've also seen some people point out the explicitly slapstick quality of the game, both as a highlight and to uphold it as good immersive sim design. The goofiness is very played up: hand sanitizer is a flammable vapor, so you can throw a lighter at a hand sanitizer to create a fireball. Black pepper stuns guards into coughing fits, bananas and soap bars create slip hazards. This is great!
What got me thinking about slapstick though, is it's the other way around from how Skin Deep is described. It's not a good immersive sim because it's slapstick, to be slapstick it has to be an immersive sim. Or, a little more broadly, slapstick requires simulation.
Hitman (broadly but mostly definitely the 2016+ iteration) is a black comedy. It has many jokes and ironic ways to kill your insufferably rich targets. It is also rife with slapstick, because it has a simulation. When you throw an object, if you have a target locked on, 47 will throw the object with a powerful overhand throw that stuns or knocks out the victim. If you don't have a target locked on, or sometimes your finger slips and you release the lock as you throw the object, he casually underhand tosses it in the general direction. When this is a a knife, or explosive rubber duck, this is funny. If you lock onto the wrong target, this is funny!
I am taking a broad view of 'simulation' here. I don't always mean physics or complex interactions. For these purposes, a simulation is any system of rules that the game and player follow in a rigid way. This surely can mean anything, and it does! Hitman has slapstick comedy when you wear a flamingo mascot outfit into the advanced robotics weapons testing room, and a guard sees you and shouts "What the..?!". The outfit and guard rules collide into a funny visual gag.
In My Summer Car, a masterpiece about being a dirtbag Finnish teenager building a car in rural '90s Finland, you have many bodily function meters like sleep and urine that govern what you get up to aside from building the eponymous car. The game allows you to punch things, which of course increases your thirst meter, and you could literally punch so much that you died of thirst. A strategy I employ frequently to quickly get my meters back in check is get clean in the sauna while freely peeing. In fact, there's seemingly no downside to peeing anywhere you like in the game, and it's always funny.
Physics is a big source of slapstick comedy of course – Goat Simulator could be the start and end of that argument. But hours of goofing off in Halo have proven even games with pretty straightforward physics can be hilarious, see also the videos of NPCs in Oblivion being caught in dungeon traps.
A huge amount of videogame slapstick comedy comes from more abstract/rules-based simulations than physics engines. The Sims is probably the crowned champion here, but I'd put forth games like Dwarf Fortress here as well.