I'm sure that when you arrange the music for a show as big as Glee, a show that sells approximately 2.2 billion songs on iTunes per episode (thanks again for the Warblers album, btw), it's easy to get a little big for your britches and assume that nobody will notice or care about the one week when you were feeling tired and, rather than work out a song yourself, decided to lift a cover from a random musician who most of your viewers have never even heard of. Only — one problem — when you did decide to do this with a folksy cover of Sir Mix-A-Lot's "Baby Got Back," people definitely noticed because, uh-oh, the performer you ripped off — Jonathan Coulton — happens to have a pretty big fan base. Sorry, Glee. You've been caught by the internet.
Posted above is the Glee cover of "Baby Got Back" and posted here is the cover composed and released by Coulton in 2005 under the creative commons license, which stipulates that the song could be shared or remixed for free, but that the work ultimately had to be attributed back to Coulton and that it was unavailable for commercial use. Glee allegedly ignored all of this:
If Coulton's cover was just another one of those cutesy acoustic versions of rap songs that white people are so fond of making, it could be argued that the similarities are just a coincidence, but in this case, Coulton composed his own melody and added his own lyrics, which also happen to occur in the Glee version. (Somehow I don't think that the "Johnny C's in trouble" line — found at the 2:17 mark on the Glee version — was pulled from the Sir Mix-A-Lot original.)
No response yet from the folks at Glee, but if they're looking for excuses, they could probably just use Vanilla Ice's from the "Ice Ice Baby" days. I doubt anyone will notice.