There are three precise criteria for measuring a Big Lipped Alligator Moment:
1) Appears out of Nowhere —
The plot comes to a halt as the scene takes its spot in the running time. There can't be any Foreshadowing and it can't take a logical place in the plot (e.g., coming across a trap while Storming The Castle is not random, but expected.)
2) Strange in Context —
The fictional setting, characters and narrative devices have to be at odds with the scene. In that regard, World Building moments, strange personalities and a surreal story structure that can explain its origin are exempt from this trope. For instance, All Just a Dream gives a good reason as using the trope tends to go hand-in-hand with the surreal (although for some genres and franchises, using the scenario of All Just a Dream itself may qualify).
3) Never Mentioned Again —
Now even important scenes are rarely mentioned later on in a film, the reason is you don't want a story to be telling you something you already knew 10 minutes ago. What this means is that upon leaving this scene the plot can suddenly start up again. Compare the Wacky Wayside Tribe.