You know how some furniture looks like solid oak or maple until it gets chipped and reveals itself to be nothing more than some cheap particle-board covered with a thin layer of fancy wood? That thin layer is called a veneer.
A veneer can be anything that makes something look more elegant or attractive than it is. Originally it was a furniture word, but over time its meaning expanded. If someone smiles at you while making some passive-aggressive remark, like, "Gee, you actually look really nice today," you could say that her inner meanness is showing through her veneer of sweetness.
