A high-ranking NCO (E-8, E-9) dressed in either a service uniform or dress uniform. The rank ensignias on the arm are so large and gaudy (and cool) they resemble the stripes of a zebra. Thus, zebra arm.
A smug, yet well recieved reference to the unit's top enlisted.
"Holy shit SSGT, looks like its zebra arm night here in NCO Club!"
"Damn Private! I can't help you with this and nor can the first shirt. You're going have to see the Zebra for this."