When a memory is triggered by something you saw on a South Park episode, i.e., their parodies of "A Perfect Storm" or "The Day After Tomorrow". This moment occurs when the movie you're watching is serious or melodramatic in nature thereby causing you to giggle while your friends look at you like you've lost your mind.
"Wow, "The Perfect Storm" sure was a real tearjerker"
(giggle, chuckle, snicker)
"Dude, what are you laughing at?"
"Sorry man, but I just had a South Park moment when the smug cloud rolled into town during George Clooney's speech in LA and everything got destroyed"