Free race modes allow you to set up multi-class races with you driving faster cars (ie. Le Mans prototypes) taking over slower stock sports cars or even microcars.
Take a Nissan GT-R LM Nismo, a front-wheel-drive Joke Le Mans Prototype in real life that failed to finish Le Mans, and put it in a race full of FWD cars from hot hatches to touring cars. Hilarity Ensues as it outpowers everyone.
The Peel P50 and Trident are not-especially-rare three-wheeled cars that can manage about 30mph under good conditions and, stock, are generally a bit of a joke. That is until you put a high-powered engine in them and watch as it pegs about 200mph. Then Forza's hilariously broken physics for it kicks in as the engine desperately tries to keep these tiny Noddy cars upright, even as it resolutely does its best to go sideways.
When the Toyota AE86 came back, it had an... interestingshifting animation. Due to the game's rating, it was silently fixed a week later, though.
In the Series 16 and Series 19 streams, the Tommy Bargains section contains some funny quotes regarding the in-game world.
In Top Gear Horizon Special, the 2nd chapter "Faster Than 87.2" starts with a segment where the Stig ends up "borrowing" Chris Harris' BMW 1M much to the latter's disdain.
Chris Harris: Ooh, a BMW 1M, great car- Hang on... THAT'S MY BMW 1M!Seriously, not funny! Who gave Stig the keys? I mean, I literally just cleaned it! Now it's going to smell of onions. (Beat) Eau de Stig...
Forza Horizon 5
After Fiesta de la Luna in the Canyon Expedition, the player is tasked with doing a speed trap and a danger sign. The vehicle being used? The float from the festival.
During this same segment, the player gets tailed by a news chopper that comments that the speed of the float you're driving is as fast as "the handsome young man" at the fiesta who said "hola" to her before he ran off.
Jaimin: She remembers me! She remembers me! Did you hear that?
Some of the musical car horn you can obtain can fall into this, especially since most of them double as Shout Outs to other Microsoft-owned games, meaning you can play the main theme of Minecraft or Doom's E1M1 as you drive by people in races.
If you really want to rub it into their faces, you can play the Windows XP shutdown sound as you pass people by.
Horizon Radio
Don Thompson of Horizon 3 and Horizon 4's Timeless FM quite clearly hates the Horizon Festival generally existing around him. He resents playing skill songs (saying he's more or less just playing them under duress and is going to hide under his desk while one is playing), doesn't like all the noise and fast driving, and makes it abundantly clear he's far happier in his booth listening to classical music. Even funnier, he pops up on Radio Awesome in the LEGO Speed Champions DLC, and makes his disdain for this job (playing the single song "EverythingIs Awesome") abundantly clear.
And, yes, there is a radio station in LEGO Speed Champions called Radio Awesome, and it literally only plays "Everything Is Awesome"... introduced by all the other DJs.
The two Hospital Records DJs in most Forza Horizon games, Tony "London Elektricity" Colman and Chris Goss (in real life, the founders of the label), enjoy trading banter while in the booth; London Elektricity, in particular, playing as a total Cloud Cuckoolander and exasperating Goss by picking apart things he says and, in one case, locking him outside in the car park in the snow under the impression that him waving his arms around trying to be let back in was him "having fun".
His replacement in Horizon 5, fellow Real LifeDrum and Bass musician Degs, is no less cuckoolandish, questioning some of the more unrealistic aspects of the series... well, actually just the fast travel boards. He's perfectly fine with the fact that the player can rewind time.
. Due to the game's rating, it was silently fixed a week later, though.