Chorus line quote?

Question

i know it's something like...

don't bop the hip cassie?

what's the exact line?

Answer 1

it's "don't pop your hip cassie!"

Answer 2

Don't pop the head, Cassie.

She's popping her head up and back, which is a common move seen in Las Vegas shows (remember she had just returned to New York after going to Los Angeles and then Vegas).  Zack doesn't want the dancers in his chorus line to pop their head, and he really jumps on Cassie about it.