Like double spacing after periods. I didn't know this was no longer "the cool thing to do" until I heard a guy from Slate ranting about all those "fossilized old geezers who still double space after periods" on NPR's Fresh Air one day.
Yeah, double-spacing after periods is another habit whose persistence (& stubborn defense!) constantly amazes me.
I recall it being denounced as antiquated and unnecessary back in the 80s. (There was a book, sometime around 1988 or 89, called "The Mac is Not a Typewriter" that argued vehemently against the double space when proportional fonts were used.)
And yet people who weren't even alive in 1988 are here in this room who have apparently never heard the news.
I shake my head in bewilderment.