Consider who is being described. 'Unbecoming' can imply a failure to meet expectations based on role or status. His brash comments were unbecoming of a diplomat.
Pro Tip 2/3
Cultural Nuance
'Unbecoming' might be culturally specific, relating to the social norms of a particular group or society. She found his casual dress unbecoming at the formal gala.
Pro Tip 3/3
Nuanced Criticism
Using 'unbecoming' can be a polite way to criticize someone's actions or appearance without being too harsh. His joking during the meeting was unbecoming.