Rebel Wilson & Ashley Tisdale -- Melons Out for Luau and Size Matters

Rebel Wilson's watermelons versus Ashley Tisdale's coconuts -- photo proof life (and Hollywood) ain't always fair.

Reb and Ash were sporting their custom made bras in L.A. while shooting a scene for their new sitcom, "Super Fun Night" -- which we're sure it was.

Unless, of course, you're more into grapefruit. Or bananas.