Sex/Nudity: Marty's girlfriend, Jennifer, asks him if his mom knows about them going to the lake together (implying that there might be some fooling around between them).
A movie marquee shows the title "Orgy American Style," and is seen in the background of a shot, though it is blurred and hard to notice.
An XXX cinema is seen briefly.
Marty finds George (as a teen) high in a tree spying with binoculars watching Lorraine undress (she's seen in her bra and slip).
Lorraine has "the hots" for Marty (in a 1950's way) and tells him that she's never seen underwear like he's wearing.
Biff sits behind Lorraine in the cafeteria and paws at her saying, "You know you want it. You know you want me to give it to you." She then smacks him and says, "I'm not that kind of girl." He replies, "Maybe you are and you don't know it yet." She then slaps him.
Marty tells George about his plan to get him to rescue Lorraine from Marty's staged advances. After he tells George that nice girls get upset when guys try to take advantage of them, George asks, "You mean you're going to touch her on her..." but he doesn't finish the question.
Later in a parked car with Marty, Lorraine tells him that she likes to park and that it's not her first time.
Biff tries to sexually assault Lorraine, but is stopped by George.
Lorraine shows some cleavage in her low-cut dance dress. 2/10.
Violence: Marty is blown across the room by the output of a large speaker.
Several terrorists show up and shoot Doc Brown with a machine gun and then chase Marty and shoot at him as well and crash their van into a small building.
Marty crashes the Delorean into a barn and then runs over a tree as he flees from a farmer who fires a shotgun at him (thinking he's a space alien).
Marty is hit by a car and knocked unconscious.
Lorraine smacks Biff for pawing at her.
Biff and Marty push each other in the cafeteria and get ready to punch one another, but they're stopped.
Marty trips Biff, slugs him, and then knocks down his cohorts and races outside. He accidentally knocks over several people as Biff and the others chase him. They drive through some park hedges and throw bottles and cans at him. They then try to ram him (on his skateboard) into a truck but end up crashing into it themselves.
Biff pulls Marty from a parked car and then starts to paw Lorraine while the other guys punch Marty in the gut and take him away.
George tries to throw a punch at Biff who deflects it and bends George's arm behind him. Lorraine tries to help, but Biff pushes her to the ground by her face. George then gets mad, winds up a punch, and knocks Biff out.
George pushes another student to the dance floor after he rudely cuts in on a dance with Lorraine. 5/10.
Blood/Gore: A musician has a slightly bloody bandage on his hand. Doc has a bandage on his head and for a brief moment you can see some blood. A car crashes into a truck of manure and one character spits a bit of manure out. 3/10.
Profanity: At least 5 "s" words (1 of which is 4 said at the same time), 12 damns, 8 hells, 3 asses (1 used with "hole"), 3 S.O.B.'s, and 6 uses each of "Oh my God," and "Jesus," 4 uses of "G-damn," 2 uses each of "Jesus Christ" and "My God," and 1 use each of "God" and "Oh God" as exclamations. 5/10.
Alcohol/Drugs: As an adult, Biff grabs a beer out of the fridge.
As an adult, Lorraine pours vodka into whatever she's drinking.
Lorraine's father has a beer on the table at dinner.
Lorraine takes a swig of alcohol from a flask and tells Marty that "Everybody's who anybody drinks." Marty takes it from her (commenting on how it might lead to future drinking problems) and then absentmindedly takes a swig himself.
Biff's gang drink beer.
One of Biff's cohorts tells some musicians that they "don't want to mess with no reefer addicts," and, although smoke comes from their car, there's no indication that it's marijuana.
A drunk man on a park bench holds a bottle of liquor.
Doc grabs a beer can from the trash and pours the remaining liquid into his time machine for fuel. 3/10.
Smoking: Lorraine briefly lights up a cigarette in a car.
Some musicians get out of a smokey car.
Some students smoke outside a dance.
Back to the Future is one of the best films ever made, and probably the best time-travel movie ever made. I definitely recommend you watch it. I give it 9/10.