Who's Losing Her Top?

Duh, it's Vanessa Hudgens!

The Disney starlet cruised the harbor in Sydney yesterday with pal Ashley Tisdale and boyfriend Zac Efron by her side.

But what's with the frown?  Trouble in tween paradise for Zanessa?  Too much togetherness, perhaps?  Good thing she's got Ashley to fill in for her as a hand-holding partner.  'Cause that's what friends are for...

Click below for 44 photos of the trio promoting High School Musical 3 down under.