In Case You Missed It: Kurt And Blaine Kiss On 'Glee' (Video)
In an episode that tackled bullying, Blaine asked Kurt to be his duet partner before coming clean later: he wanted to be partners so he could have an excuse to be with him. You can read the episode's recap here.
Of course, it isn't the first time Kurt kissed a guy on Glee. In November, an episode in which he confronts a highschool jock (Karofsky) for pushing him into a locker ended in a sudden kiss - from the jock!