There are two strippers shown at John's birthday party.
There is literally no sex and no nudity involved. It's all references.
A teenage boy is rumored to have herpes. He later becomes a spokesperson for herpes, and a girl with the condition is seen kissing him on the cheek.
There are rumors that the title character, John Tucker, is sexually active. One of the lead girls in the movie admits to having sex with him. The other girls make fun of her for it a lot. For example, when she says that she and John share something special, another girl says "What, that you've both been in your pants?" and when John breaks up with her later in the movie, she says that she was so upset, she couldn't even enjoy the break-up sex.
A teenage girl is talking about how sexually attractive John Tucker is and how good it feels when he wraps his arms around her. Then the girl's friend comments "Um, we all know what happens when boys get happy". Teenage girls call each other sluts and whores.
Teenage girls make references to "hooking up".
Kate's mother is portrayed as a single mom who dates countless men who eventually dump her. Kate gets upset midway through the movie and tells her mother that this is why she herself is so messed up, because her mother never showed her what a real relationship is.
Kate's friends hide a little video camera in her bra while she is getting ready to go on a date with John Tucker. One of the girls, who is portrayed as being sex-obsessed, says "Guys, he is going to find that in, like, the first five minutes!"
Two teenage girls kiss on the lips. They are not lesbians--one of the girls is trying to teach the other one how to kiss properly. A teenage boy catches them and says "Holy dramolama, kiss her again! Do it!" One of the girls calls him a "perv" and tells him to go away.
While hiding in the back of John Tucker's truck, a teenage girl finds a bra just lying there. She slips it in her pocket. When she is trying to get out of the truck in the next scene, her skirt gets stuck on one of the wheels. She ends up having to take it off and leave it stuck to the wheel. We don't see her underwear or anything, but when she gets back to her friends' car, she says "Even when I'm not dating John, he still gets me out of my pants!"
A teenage girl models her red bra and panties for three of her friends. She is intending to wear them for her boyfriend. One of the girls says "You should totally wear underwear to school".
A teenage girl says "We are SO going to neuter him!" while talking about John Tucker and getting revenge on him by taking his sexual attraction away.
A teenage girl (a cheerleader) says to a fellow cheerleader, "John loves girls on top". The girl looks at her funny and she says "On top of the pyramid! Hello!"
A teenage girl tricks John into wearing a thong and sneaking to her hotel room in them. In an unfortunate twist of events, he ends up in a random woman's bed. She screams, grabs him by the ear, and drags him out into the hallway wearing only the thong. A teenage boy sees them and says "Dude, those are for ladies!" The hallway becomes crowded with people laughing and taking his picture. His butt is clearly visible, even though he's trying to cover it up.
John convinces the entire basketball team into wearing thongs while they play. He says that it's like "letting your best friend sleep in a hammock", which can be interpreted as sexual.
A teenage boy says that his nipples hurt.
Teenagers kiss passionately and in public.