There is no such thing as a celestial body on the physics level, just atoms.
Yet RET's gravity seems to make the same distinction. Why can I not set two apples into orbit with each other?
Was that a serious question? Come on. You mean in vacuum and in space obviously, without additional modifiers?
I've actually studied the physics, which deals with gravity.
The formula which defines the pulling force between two bodies is defined as following:

G represents Gravitational constant

m1 and m2 are the masses of two bodies. and r represents the distance between the centers of the bodies. Now i fill the formula with correct units. 0,2 as m1 and m2 representing the weights of the apples in kg. 0.1 as r, the distance between the two apples(10cm, which means the apples are pretty much touching), you will get a force of
2.669536 × 10^-10 Newtons which is force so small, that it wouldn't be able to rip a single DNA molecule apart. So the force would not be able to hold apple in the orbit of other apple.
The fun thing is that you can calculate gravitational acceleration on earth with this formula. Just remove the other mass, insert earth's mass and radius+your_height and you will get the earth's theoretical gravitational acceleration on the location, which does not include the balancing by the spinning of the earth.
9.821