Basic Trope: A verbal put-down Tempts Fate - someone says that something will only happen if something else improbable happens. The improbable thing promptly happens.
Straight: Charles says "Alice and Bobwill get together...when pigs fly!" A winged piglet appears as Alice and Bob are walking down the street, holding hands. Charles is flabbergasted.
Exaggerated: Every pig in the world sprouts wings and starts flying.
Downplayed: A pig walks by with nonfunctioning wings glued to its back. This elicits chuckles from the other characters, but doesn't convince Charles of anything - at least, not until he hears that Alice and Bob have been with each other all night.
Zig Zagged: A flying pig appears. Later, it turns out it was a balloon. Except Alice and Bob really did get together, and the next morning Charlie SWEARS he sees a pig flying in a parabolic arc through the air. Then it turns out someone launched it from a catapult. Alice and Bob are still together though.
Averted: No pigs or pig parts appear when Charles makes his comment.
Enforced: The writers couldn't resist.
Lampshaded: "So...about those pigs, Charles..."
Invoked: Charles makes the comment because he wants to see flying pigs, and tempts fate in order to do so.
Exploited: Charles makes his comment, then when the winged pig comes by he catches it and shows it off as a freak show attraction for profit.
Defied: Charles cuts himself off the moment he's about to say the phrase, thinking he's going to be Tempting Fate.
Discussed: "Don't say that! You know the moment you say that, a flying pig will turn up!"
Conversed: "Yeah, yeah, and then the pigs start flying, seen it already."
Implied: The day after Charles says the phrase he sees on the news a report about a freak accident where a car crashed into a winged p- but Charles changes the channel before the reporter finishes.