This idea came to me the other day when I was listening to the Rent OBC soundtrack.
hope you enjoy it!
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"Kuuuuurt, come on. It's just lunch in the cafeteria, how long do you need to take to get ready for that." Blaine whined, sitting on his friend's bed. "I'm hungry, and Wes or Thad will probably have a fit if we're not down there in the next five minutes. " "Fine, give me two seconds and we can go." Kurt called from the bathroom.

"Dude. No, that is NOT what happened!" Jeff shrieked. "Okay sure, whatev—-HEY BLAINE AND KURT, OVER HERE!" Nick yelled to his two friends. "Ready for it?" Wes asked, standing behind the four of them, as Kurt and Blaine sat down. Kurt remained seated, looking genuinely confused. "Ready for what?" He thought, as he watched Wes return to his seat at the head of the table, and Blaine stand up next to him. The room suddenly fell quiet as Blaine started to sing:

Dearly beloved
We gather here to say our goodbyes
Here she lies
No one knew her worth
The late great daughter of Mother Earth
On these nights when we celebrate the birth

"Wait. Rent? La Vie Boheme? What the hell is going on?"Kurt thought to himself as he saw all the surrounding tables look on with smiling faces, awaiting the next part.

In that little town of Bethlehem
We raise our glass, you bet your ass to
La vie boheme

Kurt looked around still confused, as the rest of the Warblers stood up, and Blaine (in no surprise to anyone) jumped up onto the cafeteria table.

La vie boheme
La vie boheme
La vie boheme
La vie boheme

The surrounding student body were getting really into it, usually they just ignore any Warbler related outburst of song. Blaine took one look at Kurt, smiled, and continued to sing:

To days of inspiration, playing hooky, making something out of nothing
The need to express, to communicate
To going against the grain, going insane, going mad

To loving tension, no pension, to more than one dimension
To starving for attention hating convention, hating pretension
Not to mention of course hating dear old mom and dad

"Seriously, what is going on? They must've planned this."Kurt thought once again, before focusing on Blaine, and noticed he was motioning for Kurt to jump up and join him.

To riding your bike midday past the three piece suits
To fruits, to no absolutes
To Absolut, to choice, to the Village Voice
To any passing fad

By this point, Kurt was on the table with Blaine, and various other Warblers, still confused as to what was going on, but having fun and singing along at the same time. He joined in as Blaine continued:

To being an 'us' for once
Instead of a 'them'
La vie boheme
La vie boheme

Kurt heard someone clearing his throat from behind the table, he quickly turned around, only to see Headmaster Davis. "Shit."Apparently Jeff must've saw him at that moment, because, almost as if on cue, he slapped Nick's ass and said "Hey mister, she's my sister"
Wes immediately turned around, and said "Headmaster, you're early this year…you usually barge in after Blaine sings "…Mucho Masturbation."Kurt once again looked incredibly confused. "So it IS an annual thing, why the hell didn't anyone tell me?" Blaine looked up, and saw his best friend's puzzled face. He gave a look as to say "I'll explain later."