Reddit has a page for Librarians, actually several, but this is the one that I read daily. And someone asked for people to post their most embarrassing moment(s). And boy, did we reply!
https://www.reddit.com/r/Libraries/comments/1hwl1az/embarrassing_moments_as_library_professionals/
https://www.reddit.com/r/Libraries/comments/1hwl1az/embarrassing_moments_as_library_professionals/