…Hill Valley… 
It would give the famous Scotty line “It’s green!” a whole new meaning…
Another one from Back to the Future III. When Marty McFly travels back to the 19th Century, he gives his name as “Clint Eastwood”. In the climax of the movie, he drives the train off the end of the unfinished bridge and into the canyon.
Back in the 20th Century, the characters pass by a bridge. A sign shows the canyon to be named “Eastwood Gulch”.
Not a joke, per se, but I did love one particular subtle trick in Alien Nation.
You see George, one of the aliens on the other side of a window between offices. He’s talking to his partner Sykes. As they talk, George takes a container of mustard and squeezes it. You cannot see where it is going. The conversation continues and they move on. You now see that George is holding a cup of coffee.
Middleman is chock full of subtle (and not so subtle) references to movies and pop culture. For example, one time they introduce themselves as Alexander Scott and Kelly Robinson. Another time, the name of the head of the NASA people who show up to clean up after an alien device lands is Lethbridge-Stewart. In an episode about the Titanic, there’s a cut to the Southampton High School, with a sign identifying their sports teams as “The Fighting Icebergs.”
He’s a sailor people. What do you think he gets on shore leave?
Shaved with a rusty razor?
This is really subtle and I’m not sure if the Disney people meant it this way, but it makes me giggle anyway.
In Mickey’s Christmas Carol, one of the beginning scenes shows the Three Little Pigs singing Christmas carols around a lamppost. Later, when the Ghost of Christmas Present appears, one of the things he shows and mentions is suckling pig. Then later, at the end, we see the pigs again, chasing each other through the street …
… but there are only two of them!
Last night I’m watching Raffles starring my movie boyfriend, Ronald Colman. He’s sitting at dinner when a Scotland Yard detective comes to call. (Of course Scotland Yard doesn’t know that Raffles is, in fact, the Amateur Cracksman jewel thief.)
The setup may not be word for word, but the payoff is:
Scotland Yard: "There’s *robbers *in the neighborhood!
Raffles: Robbers?
SC: Well, a robber.
R: A?
SC: Aye.
R: Oh.
You have to say it out loud.
I’m sure the Disney people DID intend these, both from Who Framed Roger Rabbit
In Toontown, there’s a poster in the background for “Porky’s All-Beef Sausage”.
Think about it.
Also, one of the vehicles that Eddie’s car has run into in the suddenly-appearing downtown is a truck carrying “Acme Over-Used Gags”.
Not merely Used Gags, but Over-Used Gags.
Also, right after Eddie enters Toontown, the massed inhabitants start singing “Smile, Darn Ya, Smile”*. If you look to the lower right corner of the screen you see a pie with the head of a cow protruding from it.
It’s a Cow-Pie!
If you listen, you can even hear Eddie’s car running over it.
*The use of this song alone is, I think, an in-joke. It’s the title of an early black and white Warner Brothers cartoon from the 1930s, featuring a character named Foxy. Foxy is as close to a Mickey Mouse clone as you can get. He only differs in having slightly pointed ears and a bushy tail. Otherwise, he’s mickey, right down to his clothes. And he has a similarly Minnie-esque girlfriend. As often happened, the cartoon title is the same as that of the song in it. I can’t help but think that Foxy was an attempt to tweak Disney’s nose. And Zemeckis’ use of him was another tweak.
In the original “The Three Little Pigs” (1933) there is also a picture of a string of sausage links hanging on the wall with the caption “Father.”
A tattoo?
I always thought it was a hangover, too.
Similarly, in Forgetting Sarah Marshall:
Hotel Employee: I have a question for you real quick. What did you think of my demo? Did you get it?
Rock Star: I was gonna listen to that, but then, um, I just carried on living my life.
Well, this one’s pretty widely known, but: in Gremlins, when Mr. Peltzer is at the inventor’s convention/show/whatever and is calling home, behind him you can see what appears to be an H.G. Welles-esque “Time Machine”. The shot cuts to the other end of the conversation, and when we return to the convention, the time machine is gone; all that’s left is some smoke and some people looking baffled.
As long as someone mentioned Back to the Future, remember who the “Twin Pines” at the mall belonged to? Doc Brown reminisces that, “This whole area used to be Old Man Peabody’s farm.” It’s a reference to “Mr. Peabody”, which was the name of a time-traveling dog in a segment on “The Rocky and Bullwinkle Show”. They also gave farmer Peabody’s son the name “Sherman” in BTTF, which was the name of Mr. Peabody’s boy companion, but the name isn’t mentioned in the movie.
How about that, two subtle jokes about time travel!
I had always assumed Scotty’s need for help while on shore leave was a reference to the gag in Trouble with Tribbles. Scotty just wanted to stay on board and read his technical journals, but Kirk insisted he go on shore leave. We all know what happened then.
My favorite tiny bit is in *My Cousin Vinny. *Vinny’s a city boy stuck in the country. He can’t sleep it’s so quiet. Due to various plot machinations he gets sent to jail, where there’s a split-second shot of him sleeping peacefully during a riot.
In Hot Fuzz, Nicholas Angel is referred in a newspaper headline as the short arm of the law.