Okay I'm looking for a Blaine/ Kurt fic. I remember that Kurt goes to Dalton and is a Warbler. New Directions invites the Warblers to McKinley for a mini concert. Something happened between Blaine and Kurt which leads to Kurt depressedly listening to his iPod on the bus back to Dalton. I remember that at the rehersal after the concert thing Kurt wears his Cheerios sweatpants and everyone is surprised and someone says something along the lines of "Kurt did you know you have 'McKinley Cheerios' written on your ass?"
There may also have been a little singer exchange program where New Directions gives their countertenor (Kurt) to the Warblers, who in turn give their countertenor. The Warbler countertenor was in love with Rachel and he didn't like to sit on chairs the normal also he mapped out McKinley's air ducts. Oh and I remember that Rachel dressed up as a guy and spied on the Warblers. The countertenor asked his friend if he was gay because he was attached to Rachel in drag ( not knowing it was a girl).
These may be two different fics but i think they are the same. I hope this is enough information.