To be fair, him walking around in a mess is enough to get him court-martialled if I remember correctly. While KTKM can get into trouble for threatening a superior officer as you've said, she is also reminding him to act as befits his position.
Now, go wash your face and shave your beard.It's grooming.We are not your elder sisters nor your mother.If you trouble Ooicchi too much,Good morning, everyone.I'll make you scrap at the bottom of the sea, 'kay?Refers to Ooi's night battle lineI'm not telling you to be stylish.Since that day, he's become completely neat, y'see.