The student's striking audaciousness disturbed long-standing social hierarchies on campus.

Audaciousness means showing a willingness to take surprisingly bold risks; daring. Timidness (or timidity) means showing a lack of courage or confidence, fearfulness, which is the direct opposite. Boldness and fearlessness are synonyms of audaciousness; insightfulness means having or showing an accurate understanding. Therefore, timidness is the correct antonym.