One time I was DMing a campaign where the players walked into that tavern every campaign has and one of the patrons was a Mindflayer wearing a very bad human disguise who insisted his name was Johnald Humanman. And they were just like "Oh, okay. Well, that's his business" and didn't interact with Johnald Humanman at all.
I planned for a lot of eventualities but I never planned for a D&D party being polite
I once had a DM tell us that we completed a quest line about 3 sessions earlier than he expected because we got told by a group of lizardfolk that “nobody goes to that part of the swamp” and all went “huh, ok! Thanks for the warning” and just didn’t go