I'm not sure who the first person to say "Hakuna Machado" was. It's been pretty widely spread, including both signs in the stands and this awesome picture by Camden Chat's resident photoshop expert, Marylander. Machado himself has been spotted wearing a shirt with the phrase on it around the Orioles clubhouse.
Now the MLB Fan Cave guys have jumped onto the Hakuna Machado train and created this enjoyable video, complete with customized lyrics and appearances from Manny and other Orioles. The video runs about a minute and a half and is worth watching all the way through if only for the perfomance by Tommy Hunter, who appears near the end.
If you're on board with the Hakuna Machado phrase, you can also vote for it as the last giveaway shirt of the season. It was submitted by O's fan Tiffany Lin as part of a contest.