Accidental Truth/Playing With

Basic Trope: Someone says something that they believe to be a lie, but it then turns out to be true.
 * Straight: Fiona claims that Gordon's girlfriend is cheating on him to break them up, and it turns out that the girlfriend really is.
 * Exaggerated: Despite it being completely implausible, Fiona swears the strongest oaths she can think of that Gordon's girlfriend is sleeping with the entire football team, even inventing specific times and dates for it all. Every word turns out to be true.
 * Justified: Fiona is later told that she's psychic.
 * Inverted: Fiona tries to tell the truth, but is revealed to be incorrect.
 * Subverted: Fiona tells Gordon that his girlfriend is cheating on him, and then breathes a sigh of relief when Gordon finds his girlfriend in a compromising position. However, the girlfriend has a perfectly reasonable explanation for it, and Gordon realises that Fiona was lying.
 * Double Subverted: ...until Fiona manages to point out a flaw with the girlfriend's story that Gordon overlooked.
 * Parodied: Fiona feels free to tell whatever lies she likes, confident that as the main character, this trope will save her.
 * Deconstructed: Fiona lies about Gordon's girlfriend cheating on him. Even when it turns out to be true, Gordon breaks off ties with her due to her untrustworthiness.
 * Reconstructed: The fact that neither Gordon nor Fiona actually believed Gordon's girlfriend was cheating on him becomes an In Joke between them.
 * Zig Zagged: Fiona accuses Gordon's girlfriend of cheating. Gordon and Fiona catch her in a compromising position, but witnesses, and Fiona, claim it's Not What It Looks Like. It later turns out she was cheating, or was she, as the same situation happens again. Finally it's revealed she is, in fact, cheating on Gordon.
 * Averted: Fiona pretends that Gordon's girlfriend is cheating on him, but it simply isn't true.
 * Enforced: The execs have decided that there needs to be a Very Special Episode about lying, but have also decreed that Status Quo Is God. As such, the writers need a plot in which Fiona tells a lie, but nothing comes of it, and this is the only thing they can find -- even if it does break the Aesop to have Fiona get away with it.
 * Lampshaded: "Apparently I'm more honest than I thought."
 * Invoked: Fiona pretends that Gordon's girlfriend is cheating on him, and one of Fiona's friends, realising that she's going to get caught out, rushes off to seduce the girlfriend so that Fiona's accusation comes true.
 * Exploited: "Hey, Fiona -- if the lies you tell keep turning out to be true, could you tell a few lies about my bank statement?"
 * Defied: Gordon's girlfriend suspects that Fiona will accuse her of cheating on him, and makes sure she has plenty of witnesses to testify that she isn't.
 * Discussed: "This isn't a sitcom. If you tell a lie, reality isn't going to magically rearrange itself just to save you from being caught."
 * Conversed: "Nah, they can't have the main character get caught out in a lie like that. Just watch -- they'll build up the drama, and then reveal that it was actually true all along."

Is everything OK? Yeah, it's definitely not like I lost the link to Accidental Truth or anything-- oh, there it is!-- I mean, it was here all along.