It's not something that one should do all the time just to be a dick but there are times where it's warranted to tell someone to RTFM, or maybe even figure it out for themselves because often that's the best way to learn a given thing.
This guy whose computer I end up fixing at least three or four times a year, if not more often could do with a dose of RTFM if reading the manual would do any good. He doesn't even seem to understand the most basic computing terminology, so it all has to be explained to him repeatedly to the point of frustration. He constantly gets into shit he has no business being in and fucking things up, installing every single program he finds on the internet.
It got to the point where I made an Acronis backup image of his hard drive because it's far easier to restore that than it is to have to reinstall his OS every two or three months. Just a couple weeks ago, right after I'd gotten done restoring his image I caught him trying to install some youtube downloader thinking that he was actually installing youtube like it's a piece of software. After explaining to him that youtube wasn't something that had to be installed and making a bookmark to the actual site for him. There have been times where there were like 30 browser toolbars running and he was wondering why his computer was so slow.
All of this wouldn't be so bad if he'd learn from his mistakes but he doesn't, he keeps blindly doing the same things over and over and over again and even learning new ones along the way, and his kids aren't much better than he is either, always installing shit they have no idea what any of it even does and all the free toolbars that go along with it. They keep paying me to fix this shit so I can't really complain too much but you'd think they'd get tired of paying me to fix the same crap so many times and learn from their mistakes.
So yes some people should be told to RTFM when they need to be for their own good, but at the same time it doesn't hurt to help people who you know are going to learn from whatever you teach them either.