Make it real loud!
Put your hands up, make 'em touch, touch

[Verse 2]
I've overheard your theory "Nostalgia's for geeks"
I guess sir, if you say so, some of us just like to read
One second I'm a Koons, then suddenly the Koons is me
Pop culture was in art, now art’s in pop culture, in me...

Huh? Rap Genius explains:

Jeff Koons is an artist who was born decades before Gaga, and is known for his bizarre sculptures. He’s one of the many artists collaborating with her on ARTPOP’s transmedia experience.

This is up her alley:

Lady Gaga used to be only an admirer of artists. Now she’s the artist, just like that.

A popular interpretation of this line is that she is saying “kunst”, the German word for “art”. Once an artie, now the art.

Since Gaga has a thing for German, this double meaning is likely intentional.

Side Note: The double meaning is NOT intentional in this line that the radio was hyper-censoring right after its release.

Don’t worry, Nicki Minaj knows that feeling.

(Lady Gaga performing this line at the MTV 2013 VMAS. On the left is Jeff Koons' piece ‘Gazing Ball’)

Oh, I get it. Cool!

From the 2013 MTV VMAs: