With Javascript disabled the aspect that is a pet peeve isn't some broken functionality of a site (which one would expect) but when a considerable amount of sites add a blank overlay until JS and/or cookies are enabled.

And not the scenario where JS is responsible for loading the content but literally when it's just an arbitrary blank viewport-encompassing element covering the already loaded content—all so the site can then add some animation and remove the overlay when they feel the content should be shown.

It's ridiculous for functionality. When I overhauled a wiki for a project it similarly added such an overlay and I promptly removed it. Nothing on the wiki beside the search was functionally broken without JS yet it required both JS and cookies to be enabled before a user could view anything.