Treading carefully, as this may be on the borders of EN World good-taste policy. Also, I'm not sure if this one converts well from spoken word to text.
Several years ago, we were playing a Forgotten Realms campaign set in Mulhorand. Another player's character was Neferteta, a female Cleric who'd been a bit of a tearaway before reforming and joining the priesthood. My character, a warlock called Ismalith, was her brother, and we quickly settled into a typically bitchy brother-sister relationship roleplay-wise.
Ismalith tended to tease Neferteta by telling the rest of the party scurrilous rumours about her, including expanding upon the "mis-spent youth" element to suggest that she was actually a former temple prostitute. It was just a bit of background role-play, until we came to be exploring an ancient tomb, and some of the other players were talking about whether to open the ornate coffins inside. At which point, I piped up, in-character:
Ismalith: "You really should stop using that word around Neferteta. It gives her nasty flashbacks to her youth, reminding her of what she used to get asked to do at the temple."
Everyone else, mystified: "What word?"
Ismalith: "Sarcophagi."
After a couple of mystified seconds, light dawned and the session more or less collapsed for the next twenty minutes.
Even to this day, none of those who were present can hear a DM mention "sarcophagi" in a description without a giggle, and whilst I wasn't there at the event, a couple of the players reported having brought a convention LFR table to a halt by collapsing in giggles for ten minutes after the word was mentioned, and then having to try and explain to the rest of the players why they were laughing.