Double clicking on the web is extremely common with older less technically adept users. This same cohort is also the most susceptible to scams.
This. I have told my eighty-year-old parents this many times over the years, but it doesn't seem to stick.
Another obvious case of double click is to select all text in a given area. This one is a bit more obscure though.
Edit: Actually that's generally I guess triple click. Double to select a word.