Disapproval is often expressed through body language, such as frowning or shaking one's head. His furrowed brow showed his disapproval before he even spoke.
Pro Tip 2/3
Social Context
In some cultures, overt disapproval can be seen as rude; it's often conveyed more subtly. Instead of criticizing, she gave a faint smile of disapproval.
Pro Tip 3/3
Mild vs. Strong
'Disapproval' could range from a mild dislike to strong opposition, depending on context. There was a note of disapproval in his voice, but he said nothing.