In most skits whenever an unexpected result occurs, a bemused character will respond with "Huh, neat."
Most Pokémon videos will feature a Shuckle eagerly waiting to see what special ability/evolution he'll have (as of Gen 8, still nothing). Other Pokémon will either pity him or take advantage of him while he remains blissfully unaware.
FreedomToons: If a video is about gun control, then expect the gun ban in Australia to be mentioned.
When Red Army first acquires their jeep, its radio is blasting loud polka-style Tejuano music without any way to shut it off. Throughout the series, polka music gradually rising in volume becomes an indication that Red Army is about to appear.
Also, anytime the tank fires a shot, any character nearby will shout "SON OF A BITCH!"
Tucker replying to any possible innuendo with "Bowchickabowwow".
Sister's odd stories ending with somebody else responding by saying "Yeah! Wait, what?"
Sarge attempting to get Grif killed for the team.
Church's inability to hit anything with a sniper rifle. He can't even shoot down a guy point blank.
Tucker's inability to actually obtain a sniper rifle.
"That doesn't seem physically possible!"
Grif and Simmons feuding over the shotgun seat of the Warthog (despite the fact that Grif usually drives and Simmons takes the mounted turret, leaving Sarge for shotgun).
Caboose persistently claiming he is Church's best friend.
Caboose accidentally killing his own teammates.
Sarge's passionate hatred of everything blue-coloured, leading to some very Insane Troll Logic plans.
Donut making anything that can be misconstrued as a double entendre sound like one.
Lopez never being understood by anyone due to speaking in robotic monotone Spanish.
Notable in that it was effectively weaponized once. Grif encounters Gene fighting Simmons in Season 15, and the two look and sound alike. It's only after Simmons correctly answers with "It's still one of life's great mysteries" that Grif blasts Gene off a cliff.
In "The Singularity", Mental Time Travel allows Donut to go back to any point in history. Naturally, he ends reliving the moment Agent Washington shot him at the end of "The Recreation" quite a few times.
In Extra Credits: It was Walpole. (Referring to financier Robert Walpole, who may have very well been the first Prime Minister from his influence.) He shows up in among other things the Crusade videos, and as the assasin of one of the Roman Emperors during the 3rd Century Crisis.
Every appearance of Adeptus Mechanicus is accompanied by some reference to toasters.
Horus is always referred to as "F*cking Horus".
Karamazov replies to his right hand man's every sentence with "Be quiet, Dominique!"
Dominique really wants to get some sandpaper cigarettes, and no one ever has any or want to fetch them for him.
Every time Fabulous Custodes appear, they want to take over Kitten's position as Emperor's caretaker. Every time, the Emperor is freaked out by the possibility.
In Rick's Minecraft Tales, creepers are ALWAYS drawn flopping back and forth with over-the-top angry faces. Also, the distorted faces people make, the way Nancy goes LO-LA-LA-LA-LA-LA, that thing with the animal floating away aand blowing up, wow, I've lost count!
Ultra Fast Pony uses "14 Hours Later..." for scene transitions, even where it makes no sense. Also, every time Fantastic Racism comes up in the series, the subtitles assure us "I swear I'm not racist." Every time Mayor Mare gives a speech, a mysterious voice calls from the crowd to heckle her.
Madness Combat: Generally speaking, anyone who smokes onscreen is guaranteed to die. Deimos was no exception.
Characters in Petera Dzive that drink (or sometimes even touch) a bottle of booze will often pass out and wake up naked in inexplicable places. Double Subversion occurs in episode 16, where the main character Peter wakes up naked and grabs a bottle of booze. He suddenly wakes up fully clothed, only to pick up another bottle and wake up naked again.
The Most Popular Girls in School: Whether or not Ashley Katchadourian is supposed to watch the door, Brittnay being told she gives sub-par hand jobs, stuff happening in the 3rd grade, among lots others.
Weiss being bamboozled by someone Flash Stepping in front of her. First with Ruby, and then with Penny. Also with Weiss, everyone except her being greeted normally - most characters call her "Ice Queen", or "Snow Angel" if they're feeling gracious.
Jaune getting launched into the air, either by catapult, by Deathstalker, or by rocket locker.
TheInvertedShadow's Lyrish series: If there's a TV screen in the room, eventually it will start playing anywhere from three to five random video clips in a row that never last more than two seconds. Material ranges from 2 Stupid Dogs to Starlight Glimmer yelling "I wasfrozentoday!"