There's a thread about Irritating Things on Websites [webmasterworld.com]. But fair's fair: how about irritating things that visitors do? I don't mean things like "be a Ukrainian robot". That goes without saying. I mean like...
Last time I processed logs, I discovered I'd inadvertently locked out a human thanks to a mistake in a RewriteRule. Ordinarily this would make me feel bad. This time it didn't. And it wasn't just because the offending visitor came from Vietnam via google translate, though I realize this would be plenty for some people. This particular translation request came after a search, which was included in the referer. It was the search that riled me.
If you lean toward information rather than commerce, you've seen them. The ones where the searcher copies the full literal text of an exam question or homework assignment, down to the last "compare and contrast" or final question mark, and pastes it into the search box.
Grr. It doesn't do me any harm, and it's never a high percentage of requests. But if I could turn them in I would happily do so. What ever happened to "Don't ask the website to do your homework for you"?