Message Boards in general or the Internet and websites in general?
If Message Boards:
Those that make you log in to view for insignificant forums. Sure, those with a good reason can use it, like for forums about sensitive issues and certain opinions, but I am sure as heck a general gaming, general chat or website design forum does not need 'Guests have to log in mode'.
Too many forums. I counted over 500 on one site before, and even with it being official, it was overkill with forums for topics no one cared about, wanted to discuss or ever actually discussed.
Certain rule sets on large forums. As in, how some large forums are pretty much dictatorships where anyone with even a different opinion gets banned.
How some forums (Webmaster World) give different content to search engines than real guests.
The hostility of some forum veterans to new users and treating them like criminals pretty much (like this sterotype:
http://redwing.hutman.net/%7Emreed/w.../xenophobe.htm).
If internet sites:
Anything with background music. That's why I, 99.9% of the time have to option set on 'Mute'.
Blink tags, marquees, right click 'protection' scripts, the usual junk. Which is why I blocked parsing of blink tags in Mozilla FireFox on my computer.
Horrible ads. Pop ups and such. And worse, how some sites for some reason let virus creators advertise on their site with auto install malware. I mean, why do so many sites let that happen?
Services where the admins and moderators haven't bothered checking or going online for like 3 years. I know a such example, where everything went wrong, and the staff just vanished pretty much forever.
Shock images and videos. Guess why...