The actual episode or storyline you're referring to seems to be confused. However, considering "The Line of Duty" isn't directly associated with Doctor Who in a well-known context (it's a British police drama series), I assume there might be confusion. If we discuss Missy's appearance and actions in episodes like "The Husbands of River Song," "The Master's Reappearance" across various seasons, or similar dramatic turns, Missy consistently brings drama and intrigue.
As they made their way back to their makeshift camp, Missy couldn't help but tease Dr. Johnson about his, ahem, "booner" (a colloquial term for a rather embarrassing and painful injury). Dr. Johnson chuckled, despite his discomfort, and playfully shot back, "Well, at least I'm providing entertainment."