I just rewatched The Nice Guys last night and I had forgotten how funny it was. What got me was when Holly, after being corrected for saying "whores and stuff," later corrected a woman who said "...anal and stuff." Holly said, "don't say 'and stuff.' Just say 'they're doing anal.'"
Another running gag that stick out, among many, is in Airplane! when someone asks, "[something]? What is it?" and the other person gives the simple definition of the word and says, "but that's not important right now."
What other callbacks or running gags are memorable to you?