You're mid-sentence, reaching for a word that you *know* you know, and instead your mouth produces something that sounds like you've never encountered language before. Your brain is screaming the definition at you—"it's that thing, you know, the opposite of... of..." —while your listener's face slowly hardens into the expression of someone waiting for a stroke to pass. By the time the word finally arrives, three sentences later, you've lost them completely and now have to choose between explaining what you meant or just nodding and moving on like you said something profound.