Exhibit A, your honor.
Worst of all, for a director who made his name chronicling the lives of lower-middle slackers through conversation, he's garbage at dialogue. Listen to any clip of two people talking in his films. Go ahead, I'll wait. Try the conversation 36 seconds into this clip:
No, that wasn't two Speak & Spells droning about Superman with no knowledge of the rhythms of conversation, that was dialogue Kevin Smith wrote on purpose.
The One Specific Thing:
On the other hand, Smith is really, really good at monologues. Not (and this is an important distinction) dialogue; if you get two people talking in a Kevin Smith movie, it sounds like they're reading off the back of cereal boxes until the next dick joke comes around. But he really has a talent for pausing a movie and letting a character sink into a long, uninterrupted story, like Tracy Morgan's elaborate hypotheticals in Cop Out or a gripping emotional moment from Genesis Rodriguez in the absolutely execrable Tusk, a movie inspired by a dumb joke he made on a podcast. And of course, the speech he delivers as Silent Bob in Chasing Amy (an admittedly decent movie).
In Mallrats, the unexpected airplane story seems like it's building to something remarkable. It feels like it should be the climax of the movie, but it's not; it's not even the climax of that scene. It's just a long speech about a dude jerking it on a plane. And yet it's riveting, not just to the audience in the film, but to us, the watchers of the watchers themselves.