“The Full Monty” used to mean giving it your all. Now it means men stripping down to nothing.
Teabagger
I just came in to say: Hey Annie, welcome back ! So, they took off the cast of your arm, eh? Or are you typing this with your nose? 
I have a smaller cast on my arm, and I’m forcing myself to type with both hands and then make corrections!
I should be cast-free in about two weeks.
1984 was just a date in the future prior to 1949.
Welcome back!
1984.
Orwell probably enjoyed that, too.
Lolita.
MacGyver–once a Scottish surname, now a verb.
Going old school: Romeo and Juliet
Going even older school: Bible
Similarly, Trilby and her much better known counterpart, Svengali.
Governor of Alaska
Not exactly used as a title, but still its meaning has broadened recently:
“Hiking the Appalachian trail”
Ivor Novello’s last musical was Gay Is the Word. By 1950, I’m know some people were using “gay” to mean more than “happy.”
And Mr Novello himself. might well have been aware of that usage…
Wag the Dog.
From “the tail is wagging the dog.” Used to mean a small portion exercising disproportionate influence over the whole.
Now is commonly used (as per the movie) to refer to military adventures used as political cover.
Sort of going the other way. Back in the day- “The Candy Man” was your friendly neighborhood heroin pusher. Then Sammy Davis Jr. covered a song by that title from the first Willy Wonka movie and now it means a more positive, wish-fulfilling, person. (Although it’s not clear to me if the song is about candy or “candy”.) The later horror movies seem to have had no lasting effect on the term.
“All In The Family”
“Gaslight”, from the play and movie. It’s come to mean deliberately driving someone insane, especially by manipulating them into doubting their own sanity.
In one of the last episodes of West Wing, Josh Lyman said he was thinking about “hiking the Appalachian trail” but it was the wrong time of year. The meaning has so much changed since that was recorded.
“Leaving Las Vegas” used to mean simply departing from the county seat of Clark County in the state of Nevada. After the movie, it means someone who will be drinking themselves to death–or at least to oblivion–in a short period of time.
Groundhog Day was traditionally the name of a minor winter holiday on February 2, but now it’s a common metaphor for a surrealistic experience of repeating the same situation over and over and over.