His devotion to Team Starkid. This is a guy who shot to worldwide fame on an uber-popular television show, has multiple Billboard chart-toppers . . . and still takes the time to write and perform with his college theatre group.
Throwing the Starkids a closing-night party at a Las Vegas nightclub because he wasn't able to make all the shows.
His reaction to Kurt and Blaine's Big Damn Kiss; he makes no secret about how excited he is to be a part of something so groundbreaking, heaps praise upon co-star Chris Colfer and is generally as big a Klaine fan as any member of the fandom. In this day and age when many straight actors feel obliged to give an "I'm not gay, Not That There's Anything Wrong with That" speech, Darren makes jokes about how he had to "come out as straight" to his theater friends. Needless to say, he is now all but universally adored.
During the Glee Live 2011 tour, Darren and Chris Colfer did an in-character skit every night, which was written by Chris. He did ever-increasingly ridiculous things to try and get Darren to laugh. On the final night in Dublin, Darren decided to kiss Chris. The fangirls went crazy, the internet exploded, and Darren won the feud.
Performing a medley of Alan Menken songs with Lea Salonga for the man himself after he won the Hollywood Reporter / Billboard Maestro Award certainly qualifies, especially considering how Darren started out performing his songs.