Lopsided Dichotomy

""Either that kid has a lightbulb up his butt, or his colon has a great idea.""

- Dr. Cox from Scrubs, on an x-ray showing a lightbulb in a patient.

Either you're hallucinating after eating too much radioactive pizza last night, or you're reading a trope page about rhetorical comparisons like this one.

Sometimes, as a means of humour, or simply to argue for one possibility through ridicule of all possible alternatives, someone will frame a description or explanation as "either it was X highly unlikely set of circumstances, or it was Y straightforward apparent conclusion." (The X and Y can be reversed instead.)

Often associated with Deadpan Snarkers and/or First Person Smartasses.

Most often "Y straightforward apparent conclusion" is obviously the truth and the dichotomy is employed as means of snark or lampshading. However on occasion, this trope will be subverted to comic effect when the more bizarre conclusion turns out to be precisely correct instead, perhaps sometimes as An Aesop about not being too sure of yourself about what is possible and what is not.

If the characters decide that the mundane explanation is actually less plausible, it may be an Impossibly Mundane Explanation.

Sometimes also overlaps with False Dichotomy, when the ludicrous explanation isn't really the only alternative to the implied one. Talks Like a Simile is related.

Film

 * In Finding Nemo, when Dory is translating whale speech: "Okay, he either said, 'move to the back of the throat,' or he 'wants a root beer float'."
 * Groucho Marx in Monkey Business: Either this man is dead or my watch has stopped.

Live-Action TV
""Either they're going to talk to their prince, or they're going to go and eat a cheesemonkey.""
 * The page quotation from Scrubs, of course.
 * In Angel, with Lorne translating for some demons...

"Either that costs more than 25 bucks, or I'm seriously starting to doubt Steve Jobs' business strategy."
 * From House, where House talks about the iPhone:

"There's 300 of them, and 1 of us, and he's worried about their safety? He's either a pussy, or he thinks he recognizes Erin from Drunken Master 2."
 * Penn & Teller: Bullshit! used this in the college episode in response to a college rally organizer who told a counter-protestor to move away from the crowd.

Newspaper Comics
"Risk: Public humiliation and the death of thousands of innocent people. Reward: A certificate of appreciation in a handsome plastic frame."
 * Apart from the Calvin and Hobbes page image, another Calvin and Hobbes example would be Calvin saying "either mom's cooking dinner or someone got sick in the furnace duct."
 * In "The Dilbert Principle", Scott Adams describes the two possible results of a career in engineering:

"Mother: NOO! Noo: Has my mother just found my father's corpse inside of the microwave, or she is calling me for supper."
 * At the end of a Dilbert arc, Dilbert wonders why he's sitting naked in a trash can, and Dogbert explains, "Either you were killed by wild deer and we cloned you back to life from your old garbage... or... you saved a lot of money on an aboveground pool."
 * David Ramirez's prize-winning short comic, "My Little Tomoka", is protagonized by a girl who was, accidentally, named Noo. So, when her mother calls her yelling...

Recorded and Stand Up Comedy

 * George Carlin suggested something like this as a way to "wake people up": When someone asks you what time it is, you look at your watch and say, "Either it's 8:15 or Mickey has a hard-on!"

Video Games

 * In Knights of the Old Republic, if you ask HK-47 for help understanding a Jawa, he says, "Translation: 98% probability that members of the miniature organic's tribe are being held by Sand People, master. Doubtless he wishes assistance." When asked about the other two percent, he adds, "Translation: 2% probability that the miniature organic is simply looking for trouble and needs to be blasted. That may be wishful thinking on my part, master."
 * At the end of Quest for Glory IV, the hero is surrounded by the thankful people of the land after (like the past three games) completing yet another heroic quest. Cue Erasmus and Fenrus taking that moment to scry on the hero, with Fenrus commenting that "It's either an award ceremony or a lynch mob."

Web Comics
"Roy: Either you're trying to tell me that my body was used to make a golem, or ... actually, I can't think of any other possible interpretation."
 * Subverted in an Order of the Stick strip, when Roy (as a spirit in the Afterlife Antechamber) attempts one after his father hands him copies of Frankenstein, I Robot, Promethean: The Created and Everything You Always Wanted To Know About Your Dead Body Being Used To Make A Bone Golem (But Were Afraid To Ask) to "help [him] come to terms with the bad news".

Web Original
"Shouldn’t there be a comma in that dialogue? Or is Gay Marriage Obama a new action figure?"
 * Shittiest Editorial Cartoon uses this from time to time.

Western Animation
"Major Monogram: Good morning, Agent P. The entire Tri-State Area is becoming riddled with holes. Also, numerous light beams have been shot from Doofenshmirtz's building. Either he's having some sort of a rave, or he's the one behind all those holes."
 * Phineas and Ferb:
 * "Ask A Foolish Question":

"Major Monogram: Morning, Agent P. We've recently found surveillance footage of Doofenshmirtz buying fresh produce. We've concluded that there are two possibilities: either he's up to something sinister that is food-related, or he's cooking dinner because he's got a beautiful woman coming over and he wants to imp... Never mind, it's obviously the first thing."
 * "Meatloaf Surprise":

"Garfield: Either Jon's home or somebody put a VCR in the garbage disposal."
 * Garfield and Friends episode, "Wonderful World":

"Bart: Hey look! Is that Dad? Lisa: Either that or Batman's really let himself go."
 * From The Simpsons, when Homer stands in front of a lighthouse, causing his silhouette to be projected onto the clouds...