They're not particularly big, but not particularly small either...

YOU IDIOTS!

Sanji, you're small boobs are cute aren't they?

Palm-sized?

*Boing*

*Boing*

Hey Tiny boobs!

What, If you're turned on by excessive [boobs] you'll manifest envy

WELL YOU GUYS AREN'T EXACTLY THE STANDARD SIZE!!

This isn't relevant but of the Salad girls Fem-Sanji is definitely the only one to wear underwear neatly
I think this is referencing the original Genderbend page Oda did but I'm not exactly sure what it's trying to say, something about Sanji wearing underwear a certain way?