It's not like Daniel Tosh or his show's production team put a gun to his head and told him to come on his show and lie. Sure he may have been harassed online, but that comes with any type of video of that sort.
After watching the video, I'm even more confident it's fake. I've seen literally hundreds of people get tattoos, since my brother is a former artist and I've never seen a reaction to that degree. It doesn't mean he has a condition, it means he's a convincible psycho. Not to mention the tattoo is damn near done and no artist in their right mind would continue going through that ordeal for hours. An artist would also need to be notified prior of any problems or conditions, hence why they have you fill out paperwork and answer a series of questions. Also, if his family actually gave a tinkers damn about him they wouldn't exploit his disability. I could go on...