When Red Army first acquires their jeep, its radio is blasting loud polka 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.
It's Tejuano music, referencing Lopez being the mechanic.
Also, anytime the tank fires a shot, any character nearby will shout "SON OF A BITCH!"
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.
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.
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 Kachadorian is supposed to watch the door, as well as Brittnay being told she gives sub-par hand jobs, stuff happening in the 3rd grade, among lots others.