For the below context , I'm confused that what's funny for the underline?

Chandler: Kids, new dream... I'm in Las Vegas. (Rachel sits down to hear Chandler's dream.)

Customer: (To Rachel) Ahh, miss? More coffee?

Rachel: Ugh. (To another customer that's leaving.) Excuse me, could you give this to that guy over there? (Hands him the coffee pot.) Go ahead. (He does so.) Thank you. (To the gang.) Sorry. Okay, Las Vegas.

Chandler: Okay, so, I'm in Las Vegas... I'm Liza Minelli- (everyone laugh)