These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Adaptation Displacement: You'll usually see the film more remembered than the Broadway musical, especially with most tropes on this article applying to the movie script. The 1971 Kingston Mines Grease (pre-Broadway) itself was displaced by both, except for when it got a brief 40th anniversary revival.
Is that a teacher along as a mechanic for the illegal street aqueduct race?
Danny getting involved in school activities and doing better at his education is just as much of a sacrifice as Sandy slutting herself up and smoking for him.
We also don't know if he actually stuck to it. He pretty quickly ditches his cardigan and everything when he sees her in the cat suit.
Musical-only: Another girl has a crush on "your" guy? Punch her and show her who's the boss.
From the Chicago staging, we have Danny manipulating someone into thinking he loves her, just so he can get into the track team and make Sandy jealous over his fake "crush".
The film's version of "Beauty School Dropout" is seen by some as arguably better than the musical's version. In the original lyrics, the Teen Angel tells Frenchy there's no hope in getting through to her, and she DOESN'T return to high school.
"Funny Aneurysm" Moment: The lyrics of "Sandy" took on another tragic meaning when Hurricane Sandy hit the northeastern US in late October/early November 2012.
"Greased Lightning" can be hard to watch, knowing that Jeff Conaway suffered a back injury during the filming of it that would plague him for the rest of his life, and ultimately cause an addiction to painkillers.
Hollywood Pudgy: Although the film version still treated Jan as if she were overweight, her actress was actually far from it. They tried to downplay her figure with frumpy clothing compared to the other girls. Her figure is clearly displayed at the end of the film when she's in a summer dress. Jamie Donnelly claims that the intent was for Jan to be played as a fat, frumpy girl at the start and that she'd get more confidence and the chance to clean up nicely.
This is either averted or played straight in the stage productions, depending on the actress cast in the role. The original Broadway Jan (Garn Stephens) was actually a bit overweight. Later Jan actresses are either chubby, or simply just have slightly thicker hips and waist compared to those playing the other female characters.
Roger is referred to as a "lardass" by both Jan and Sonny in the Broadway script. His character bio also describes him as being "stocky", but most actors playing him tended to be on the thinner side, making these comments look strange. Some productions avert this and cast heavier actors in the role, which creates the effect of him and Jan being the token pair of fat kids.
Ho Yay: There is perhaps an undercurrent between Danny and Kenickie. During "Summer Nights" Putzie is seen briefly groping Kenickie who looks like he's thoroughly enjoying it. And "Greased Lightnin'" is brimming with homo-eroticism what with the butt-shots and Danny's head being in direct line to Kenickie's crotch and vice versa much of the time; the fact that the lyrics are about how much pussy they're going to get makes this a Crowning Moment of Funny. There's quite an undercurrent in the 'Will you be my second?" conversation they have just before the race.
Kenickie's head also likes to find its way in between Danny's knees during the music numbers, A LOT.
Hype Backlash: Paramount waited five years after first entering the DVD market to release Grease in that format. They also apparently spent a lot on advertising, including staging a cast reunion. Unfortunately, fans hoping Paramount put as much effort into producing bonus features found nothing but the original trailer, and a handful of interviews dragged over from the 20th Anniversary Laserdisc/VHS. They had to wait four more years for a DVD with more extras.
Just Here for Godzilla: A lot more people than you might think, care more about the songs than they do the story, the characters and by extension, the message. That's not to say that the Unfortunate Implications should be ignored, but the characters and story are so dated now, that whether fans realise it or not, it's usually the last thing that gets talked about. The songs on the other hand are so catchy and upbeat, that it shouldn't be a surprise that they've stayed this popular for so long.
One-Scene Wonder: Teen Angel for "Beauty School Dropout," played by none other than Frankie Avalon himself.
Stoic Woobie: Rizzo. Especially in her song "There Are Worse Things I Could Do".
Unfortunate Implications: To mend the rift in the relationship with the boy you like, you have to dress in revealing clothing, wear tarty make-up and talk in a husky voice. Nice.
"Did she put up a fight?" Wait a minute, did the guys just admit to being date-rapists less than 5 minutes into the movie?
Or assumed the girl played hard to get?
Danny was (in the movie, quite clearly) playing at being tough. It's not too hard to assume that they're all doing it to some extent. (Hell, Kenickie pretty blatantly reveals in the movie that Rizzo is his first)
In the original musical, besides dressing up as a "bad girl", Sandy also punches out Patty Simcox (who bears a crush on Danny) in order to impress both the guys and the Pink Ladies, and to stake her claim on Danny. Of course, this wasn't helped by Patty calling her a floozy.
The Kingston Mines version (and its remake) have Kenickie try to coax Sandy to go off with him into the woods and other places, as part of him trying to make Rizzo jealous. A few reviewers were uncomfortable with his behavior, noting that the way he strong-arms Sandy and forces her away seem to indicate him being a Domestic Abuser and potential rapist.
Values Dissonance: Jim Jacobs and Warren Casey apparently intended for Sandy's change to be seen as her becoming more free and sexually liberated, shedding the '50s "good girl" stereotype, as well as a reversal of the "bad boy becomes good" plot they'd seen in films of that era. But considering she changes just to fit in with the crowd and win Danny back, her new-found "freedom" is not without the unfortunate subtext or criticism of how it's handled.
Why Would Anyone Take Him Back?? Seriously, from what we see of Danny Zuko, at least in the stage version, he's just not worth it. Sandy should just dump him and move on. (Is this a Gender Flip of normal romance tropes, in which a boy has to "win" a girl who initially rejects him?)