His inappropriate behaviour earned plaudits from his colleagues.

'Plaudits' means praise or applause, which would not be earned by 'inappropriate behaviour'. The context demands a word meaning harsh criticism or disgrace. 'Opprobrium' means harsh criticism or censure, or the public disgrace arising from shameful conduct, which exactly matches the consequence of inappropriate behaviour. 'Sanctimoniousness' means pretended piety. 'Triumph' means victory. 'Banter' means playful exchange of remarks. Therefore, 'opprobrium' is the correct improvement.