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Bob sees Alice injecting insulin and assumes she's a junkie. He sees her with a cigarette and assumes she's addicted to marijuana. Then he sees her with a bottle of root beer and assumes she's an alcoholic...
Downplayed: Bob sees a lighter in Alice's purse and assumes she smokes (which he shrugs off, since smoking is of course legal and fairly common). She actually just likes having something to wave at concerts.
Alice was investigating Vision, a telepathic drug when her mother found it in backpack. She then concludes that Alice's powers came from this in the first place.
The two aren't mutually exclusive, after all. So if Alice is diabetic and also is a drug addict, Bob has caught her doing drugs, but doesn't know about her medical issues, he would have good reason to mistake her for junkie. Although, that's more of a 'Mistaken for junkie' in one specific instance, in that she is a junkie, she's just not using at the time Bob chooses to walk in.
Inverted: Alice is an addict and is going through withdraw after her dealer got busted and she can't get a new supply. Bob thinks her symptoms are from emerging telepathy and gives her the number of a teacher to help her deal with it.
Subverted: At first it looks like a misunderstanding then it turns out she was an addict all along.
Double Subverted: However, she is also diabetic, and at the time was only using insulin.
Parodied: Alice's medicine containers are clearly marked in big red letters, yet Bob still thinks she's an addict.
Zig Zagged: Some people recognise Alice's insulin as what it is, other people don't. Bob appears to have a selective memory.
Averted: Alice is startled by Bob walking in on her. Bob reads the label and apologizes for startling her and leaves her to dose in privacy.