The mnemonic
The Simpsons theme. The "The Simp-" to "-sons" leap is a tritone up. Danny Elfman wrote it that way on purpose so the show would have a recognizable musical fingerprint. Once you've matched the cartoon to the interval, you can't unhear it.
The other commonly-cited mnemonic is the opening of "Maria" from West Side Story, where the first two syllables are a rising tritone and the third resolves up a half-step to the perfect 5th. The resolution is the point: the tritone wants to move, and Bernstein gives it permission to.
Why it can't settle
In the key of C major, the only naturally-occurring tritone is between F and B. Sing them together and your ear immediately wants the F to fall to E and the B to rise to C. That outward resolution is what every dominant 7 chord is built around. C7 (C, E, G, B♭) contains the same tritone between E and B♭. When it resolves, E moves up to F and B♭ moves down to A. The chord lands on F major.
Every blues turnaround, every II-V-I, every classical perfect cadence runs that move. The dominant 7 is the engine; the tritone inside it is the spark.
The "devil's interval" thing
You'll see the tritone called diabolus in musica in most popular write-ups. Medieval theorists did use the phrase, but as a teaching aid for avoiding awkward melodic leaps in chant, not as a metaphysical prohibition. Nobody banned the interval. Renaissance composers used it constantly, just with the resolution worked out.
The cultural association with darkness comes from how useful the tritone is for tension. Black Sabbath built a sound around it. So did most horror scores. The interval isn't evil; it's the most efficient way in tonal music to make a listener feel that something needs to happen next.
What it gets confused with
The tritone sits between the perfect 4th (one semitone narrower) and the perfect 5th (one semitone wider). The 4th feels stable and folk-friendly. The 5th feels settled. The tritone feels like you stopped a semitone short of either of them. That unease is the giveaway.
Worth knowing: a tritone inverted is still a tritone. Six semitones up from C is F♯; six semitones up from F♯ is C, twelve semitones from where you started. The interval is its own mirror. This is also why an augmented 4th and a diminished 5th sound identical: they're the same pitch distance, spelled differently for notation reasons.
How Aubel handles it
The tritone is the last interval to unlock. By the time you get there, you've worked through the surrounding intervals and the cognitive question becomes "is this the weird one?" instead of "what is this?" which makes the recognition decision much faster. The detail screen suggests The Simpsons by default, Maria as a fallback.