What is the difference between various prepositions used with unbecoming?
unbecoming to vs unbecoming for vs unbecoming of.
And sometimes when there is no preposition at all, like conduct unbecoming an officer.
It's an adjective, and depending on what's being described, different prepositions will be appropriate. Merriam-Webster dictionary specifically includes a preposition for "conduct unbecoming to an officer". Unbecoming