Rainbow Tylenol is a YTPMV fad that was extremley popular on the video-sharing site youtube throughout the year of 2010. The video's usually consist of the original title mixed up with either the words 'Rainbow' or 'Tylenol'.
The original song that was remixed by various people was the song Rainbow Tylenol, by Kitsune^2
By May the 1st 2011, the YTPMV was uploaded numerous times, but overall, the fad was not incredibly popular. On the 28th of May, 2010 youtuber EnigmaEvocative posted the video Rainbow Trololol to youtube. The video was a remix of the original Kitsune^2 song remixed with Edward Hill's 1960's performance of Я очень рад, ведь я, наконец, возвращаюсь домой (Indeed, I am very glad that I finally am returning home). The video grew immensely popular, reaching 2,151,309 views, as of the 10th of April, 2012.
After this success, many more remixes and mashups we're created from the song. By mid-2011, the fad had more-or-less died. But there are still some remixes being created today.