Jeff Spicoli is a fictional character in Fast Times at Ridgemont High played by Sean Penn. While he is a freshman in the book, he is a senior in the film. Spicoli is a surfer dude with no job who enjoys smoking marijuana. Penn's performance is the first notable instance of the Southern California "surfer stoner" being portrayed on film (as culturally distinct from other "stoner" characters such as Pedro de Pacas (Cheech Marin), Man (Tommy Chong), Carl Spackler (Bill Murray) and Billy (Dennis Hopper)).
One of the first times the viewer sees Spicoli in the movie, he is late for Mr. Hand's U.S. History class. According to one of his classmates, he has been "stoned since the third grade." Throughout the film, Spicoli serves as the comic relief, usually opposite Mr. Hand in a series of amusing sketches. He was also late when he stayed in the food lines to get a bagel. When Mr. Hand asked him why he continually wastes his time, Jeff's response was "I don't know." Mr. Hand then wrote those words on the board for all of his classes to see, with Spicoli seemingly appreciating the recognition.
He is always short of money and does not have a job. When Brad Hamilton asks him why he doesn't have a job, Spicoli answers, "All I need are some tasty waves, a cool buzz, an' I'm fine." He purportedly received a guitar pick from Mick Jagger, whom he claims to have met after a Rolling Stones concert in Anaheim, California. His closest pals are two unnamed surfer dudes played by Eric Stoltz and Anthony Edwards. He is also friends with Ridgemont High's star football player Charles Jefferson's little brother, having played video games with him at the mall. When they were driving Charles' car to a party, Jeff crashed the car and wrecked it. They made it look as if a rival school, Lincoln High, had done it. Jeff's little brother, Curtis, thinks that he is stupid. He also owns a pair of turquoise colored Ray-Ban Wayfarer sunglasses, which he wears occasionally in Mr. Hand's class.
On the day of the prom, Mr. Hand shows up at Spicoli's house and tutors him as payback for having wasted 8 hours of his time during the school year. After the tutoring session, Jeff wonders if there's a kid like him in Mr. Hand's class every year. He also wonders if he'll pass U.S. History. Mr. Hand tells him not to worry and that he'll probably "squeak by."
At the end of the movie, it is revealed that at some point in the future he saved Brooke Shields from drowning, and was rewarded with a large amount of money. He then blew it all by hiring Van Halen to play at his birthday party.
Outtakes and TV Spinoff 
The movie omitted a few events involving Spicoli that take place in the book: A student named Louis Crowely loses his father and sister in a car crash. The next day, Spicoli walks into his journalism class and shows everyone a newspaper that has photos of the car crash ("Look at these bitchin' photos of the crash"), causing Louis to sob. It would be another month before anyone spoke to him again.
Another omission is a sequence where Spicoli gives a speech in class. He describes how Mick Jagger gave him the necklace he was wearing after they did coke together. The class, assigned to grade him, gives him a D. Also, the dean of discipline pulls a gun on Spicoli when he mistakes his bong for a shotgun. This causes the dean to be sued and fired. While attending a school talent show, Spicoli plays a loud beeping handheld football game during the acts that bore him.
Jeff Spicoli is a main character in the 1986 TV spinoff, Fast Times, where he is portrayed by Dean Cameron. The show makes references to his truancy when he shows up to Mr. Hand's class one period late. One day, he surprises Mr. Hand when he shows up early to class due to a "gnarly shark attack". His lack of money is also referenced when he tries to pay for a pizza where Linda and Stacy work (he takes some change and his brother's tooth out of his pocket).
Jeff Spicoli is the center of certain plots throughout the show's short run. In the pilot episode, Mr. Hand bets that Spicoli will screw up his class presentation. In the episode "The Last Laugh", Spicoli accepts a challenge to make Mr. Hand laugh. In "The Engagement", he starts a rumour that Mr. Hand lost an eye during World War II.
Since the TV spinoff is toned down for younger viewers, there is no reference to Jeff Spicoli's drug usage.
Cultural References 
Grand Puba, the rapper who fronted Brand Nubian, references Jeff Spicoli in the song "To The Right" ("Used to drink the Old E / Cool as Jeff Spicoli / When I play soccer with the dreads / I play goalie")
New Orleans rapper Curren$y refers to himself as "Spitta Spicoli" on his 2008 mixtape 'Fast Times at Ridgemont Fly. Like Jeff Spicoli, Curren$y is known for his frequent marijuana usage.
Dan le sac vs Scroobius Pip reference Spicoli in their track Rapper's Battle ("Sean Penn could win 10 Oscars and he'd still be Spicoli").
Das Racist reference Spicoli in their song "Puerto Rican Cousins" with the line "Holy Spicoli Batman, I'm Sean Penn!".