con, n.5 This one surprised me; I never would have guessed it was this old. The con in question is the clipped form of convention. The usage dates to the Chicago Science Fiction Convention of 1940, or Chicon.
Didn’t surprise me, but then I’ve been a science fiction fan for over half a century. Strictly speaking, the independent word con (as opposed to the suffix -con) dates to 1942 (L. Shaw, letter to Planet Stories: “Three more cheers for the 4 WS-F Con").
Edit: Undemanding can easily be antedated; I’ve found it in the Feb. 1923 Smart Set (Sarah Addington, “Another Kind of Lollypop”: “For Ellie was undemanding, clearly the daughter of her passive, dull-spirited mother and earnest, upright father...") and in the June 1915 Harper’s (Mary Heaton Vorse, “The Eyes of the Blind”: “And she had never had a string to him — she was divinely undemanding"). Edith Wharton’s 1905 novel The House of Mirth has “He found Gerty as he had left her, simple, undemanding and devoted,” but Google Books will only let me see a 1922 edition, and I can’t be sure the wording is unchanged. (It would be a lot easier to investigate this word if most of the hits weren’t bad scans of understanding.)