Clerks (1994)
After finding out that his girlfriend went down on 36 different guys before him, Quick-Stop cashier Dante tries to get back together with an old flame, who only cheated on him 8.5 times. However, after she mistakenly has sex with a corpse in a dark bathroom, she is sent to a mental institution. Also, at the funeral of his former high school girlfriend, he and Randal knock over the casket.
Sex = Death

Mallrats (1995)
Slackers T.S. and Brodie both break up with their girlfriends on the same day, then set out to get them back. Brodie has a throwaway hook-up with his ex in the elevator, but T.S. has to go on a dating game show to literally win the right to date his. Mall employee Shannon has sex with a girl who only does it as research for a book, then he tries to do the same with Brodie's girlfriend. He is arrested when the researcher is revealed to be only 15 years old.
Sex = Emotionally meaningless + Illegal

Chasing Amy (1997)
Comic artist Holden falls for a lesbian artist named Alyssa, and despite not really knowing anything about lesbians, confesses his love for her. She sleeps with him, and they are good together until he finds out that she hasn't always been a lesbian, and in fact had sex with two guys once, earning herself an unsavory nickname. When Holden suggests a three-way with his best friend -- who shows animal pornography to children -- to relieve the tension between them all, she gets mad and breaks up with him.
Sex = Complicated + Not a cure-all + Occasionally filthy

Dogma (1999)
While sex is downplayed in this religious road-trip movie, the impact of religion of sex is pretty clear. The last living relative of Jesus Christ, Bethany, is an abortion-clinic employee. One of the Muses, who inspire art, is now a strip-tease dancer. Metatron, the voice of God, has no genitals. And Bethany is impregnated by God, who is played by Alanis Morissette.
Sex = Not recommended by the Church + Less effective than immaculate conception

Jay and Silent Bob Strike Back (2001)
Tricked into helping four sexy women rob a diamond depository, Jay and Silent Bob are framed as eco-terrorists from the Coalition for Liberation of Itinerate Tree-dwellers. To make matters worse, Jay declares himself the "Master of the CLIT" and is assumed to be the ringleader.
Sex = Good for making people do what you want + Not something to brag about on camera

Jersey Girl (2004)
When publicist Ollie's wife dies in childbirth, he has to bring his daughter to work, which causes him to lose his cool and get fired. He takes a less important job, meets a video store clerk, and is caught in the shower with her by his daughter.
Sex = Potentially life-threatening (if it leads to children) + Potentially job-ruining (ditto) + Potentially boner-threatening (double ditto)

Clerks II (2006)
Dante and Randal, fired from their jobs after they burn down the Quick-Stop, are working at a Fast food place, and Dante has had a one-night stand with his manager, Becky. While preparing to get married and move to Florida with his dominating fiancee Emma, Dante realizes he is in love with Becky, and that she is pregnant and in love with him. These revelations, coupled with the performance of a donkey show at the restaurant, lead to Emma calling the whole thing off. Dante and Randal go into business together, and everyone lives happily ever after.
Sex = Love-inspiring + Mistake-averting + Friend-reuniting + Occasionally filthy + Not a problem in the workplace (depending on the species involved)

Zack and Miri Make a Porno (2008)
Faced with eviction, long-time friends Zack and Miri decide to make a porno film to sell to all of their old classmates in order to make money. But as they come to terms with the fact that they're actually going to have sex with each other, they start to realize their true feelings for one another.
Sex = Friendship-enhancing + Financially lucrative + Fun to do when you're dressed as Star Wars characters

Huh. Looks like Kevin Smith might be feeling better about sex, after all.