Basil's assumptions about Dorian he told Harry in the beginning of a novel, and his behavior Ret-Conned by Dorian - treating him with the jealousy only a lover would have the privilege for; accusing him of cruelly and intentionally playing with the feelingshe can't even know about; even complimenting him all the time which could easily make Dorian uncomfortable, weren't he blissfully ignorant; the Madonna–Whore Complex nature of his desire - though doesn't nullify his good intention, but his love doesn't come across as an idealizable one either.
Also Lord Henry. Was his corruption of Dorian a targeted attack on Dorian? Did he enjoy the results? Or was the outcome simply the result of his particulareccentricities? The novel tends to indicate he at least had intention, but whether the result was his intended outcome or not is up for debate.
Moe: Dorian, before going crazy. He starts out having a naive, childish personality that everyone around him becomes enamored with.
Moral Event Horizon: Pick from Dorian either driving his sort-of girlfriend Sybil Vane to suicide with a cruel Breaking Speech, and only feeling bad due to his own pride or stabbing Basil Hallward to death and then blackmailing his other former lover Alan into disposing of the corpse, which later drives Alan to kill himself too.
Narm: Dorian expecting the portrait to change back instantly only because he is thinking of behaving more virtuously onwards. Even if the picture would have changed as he wanted, isn't more logical to think it would have done so only after he had fulfilled his promise?
Older Than Feudalism: If we take Dorian as Adam and Eve being tempted out of the Edenic innocence. And maybe Basil as Christ.
Uniquely, occurring within the author's own writings — a lot of the famous quotes from Wilde's comedies come from the novel, and one of the major characters in Lady Windermere's Fan is an Ascended Extra mentioned in passing in the novel.
Also, Wilde's great uncle, Charles Maturin, wrote the novel "Melmoth the Wanderer" with the title character as a Flying Dutchman type who similarly keeps a portrait well-hidden, although not for Dorian's reason, only because it is dressed in antiquated clothing.
A meta-example is that the novel is somewhat inspired by the French book A Rebours, which is the "Yellow Book" Dorian is always reading.
The Penguin Classics edition's annotations note that the basis of the story, magical pictures that capture the soul or life essence of its subject's, are very old indeed. The Picture of Dorian Gray was a grim twist and deconstruction of the magical portrait trope, which would have been well known to Wilde's audience at the time of its writing.
Some Anvils Need to Be Dropped: Arguably, you could say the story contains the message that it's what's on the inside that counts, and that good looks are no excuse for being a bad person. Alternatively, it could be saying that no matter how good-looking you are, inner ugliness will always leak through to the surface.
Mr. Isaccs's characterization as a Greedy Jew was particularly anti-Semitic even for its time.
The Woobie: Basil, who has to watch Dorian Gray, the love of his life and his greatest inspiration, descend deeper and deeper into corruption against his wishes and ultimately gets murdered by him. Even The Soulless Dorian felt sorry for him.
Ho Yay: The 1976 adaptation really plays up the homoerotic subtext between the male characters, especially the scene between Dorian and Alan Campbell, where Dorian is basically trying to seduce Alan into destroying the corpse.
One-Scene Wonder: Morton Lowry as the alcoholic Adrian Singleton in the 1945 version.
Uncanny Valley: In the beginning of the 2009 film Dorian looked like he was animated.