The temporary amnesia you get when texting someone with a question or comment, and having them reply several hours or days, long after you've forgotten what it was you asked them. This also works in chat conversations where the person replies long after you closed the chat window.
Jack: Wanna check out that show on Friday? They got a two for one in the paper today.
Dana (three days later): Sure but I didn't get the paper.
Jack: Huh? What paper? Sorry. Textnesia.