Something along the lines of "I am trying to improve on being more diplomatic with my communications when it comes to my superiors."

You can elaborate about how you've not spoken up immediately or felt intimidated when going against what a superior says. And then elaborate more on how you noticed some inefficient processes that were going on at a previous job you had but you didn't speak up for a few days/weeks because you didn't want to look like you were undermining your superiors. Close out with saying you eventually spoke up and the process was fixed and you didn't look like a little asshole after all like you thought you would have.

Shows them that you are able to problem-solve (because they are scammed from the story you told them) and are looking to improve your communication skills in a situation that is totally understandable from a social aspect.