@d2718 well I came up with it after this https://chaos.social/@FlohEinstein/115592221732402728 - I had tooted something with the hashtag ISO8601, and got suggested iso8601ultras. The extreme fans of sports teams are sometimes named Ultras. And there is already a running gag "Arte Ultras", which suggests that there is an extreme fan group of the French-German culture/documentary TV channel arte (img also on my page). So, I created stickers to unite everyone who thinks ISO8601 is the best way to express date/time data