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.
Patty Simcox is portrayed as obnoxious and a loser, but aside from apparently gossiping about Rizzo's possible pregnancy (and Rizzo already being rude to nearly every character she interacts with in the film), what does she do that makes her so bad? She's a little too perky, but not really deserving of getting kicked off a bench, made fun of, have her dress lifted up in front of the whole dance, and in the musical get punched by post-makeover Sandy.
"Brusha, brusha, brusha/ Get the new Ipana/ With a brand new flavor/ It's dandy for your teeth!"
"Grease is the word/ Is the word/ That you heard/ It's got groove/ It's got meanin'!"
"I got chills! They're multiplyin'!"
"Tell me more tell me more/Like, does he have a car?
"Look at me, I'm Sandra Dee/ Lousy with virginity/ Won't go to bed 'til I'm legally wed/ I can't, I'm Sandra Dee!"
"I spend my days, just moo-oo-oo-ooning, so sad and blue..." in the stage play.
"Beauty school drop ouuuuut!"
Family-Unfriendly Aesop: 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.
Hilarious in Hindsight: During "You're the One That I Want", one ride Danny and Sandy dance around is called "Shake Shack". In 2004, a burger joint called Shake Shack opened in New York City, soon expanding nationwide.
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.
Hug and a hair comb. enough said.
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. They're so catchy and upbeat, that it shouldn't be a surprise that they've stayed this popular for so long. Many of them are played free of context so often that younger generations don't even know about the musical they came from.
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".
Unnecessary Makeover: Sandy was perfectly fine as a wholesome, sweet cheerleader, but Danny and his friends only truly accept her once she starts dressing like one of them.
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. The problem is that the rigid and repressing sexual mores that Sandy would be seen as adhering to in the beginning are no longer present in current media and haven't been for a long time; so what should have looked like her liberating herself from society's outdated expectations appeared instead to be her conforming to the now-seen-as self-destructive attitudes and behaviors of her friend group to get her boyfriend back.
Why Would Anyone Take Him Back?: 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?)