I think you're closer with the pun than with the other guess, けしからん gets used as a joking way of denouncing something (sexy) that you actually approve of, much like "rude" does in English. So pun that with Ran's name and you get the けしか藍 seen here, which is used to tag "rude" pictures of Ran on pixiv... And Komachi certainly has no right to criticize anyone else for being "rude," hence Ran's annoyance. Yeah, I have no idea about how to translate it either...