19-year-old employee shows up to work 2 hours late wearing flip-flops: 'How is this not a fireable offense?'

How clueless is he?

Many white-collar workers argue against the necessity of a "professional" wardrobe. After all, does it really matter if your sweater is too bright a color for the stuffy ladies in the break room? Does it really matter if your black slacks have a few too many pockets to be considered appropriate for the office? What's so offensive about some cargo pants when you're sitting at your desk without your pants in view for half the day anyway? 

Professional attire does serve a positive function in some workplaces. Some employees find it a lot easier to feel professional when they're wearing professional clothing, and I'm inclined to agree with them. If I'm wearing the same stuff I wear to work every day, I'm much more likely to treat my coworkers like friends than colleagues. Wearing a stuffy outfit that I would never be caught in at a regular social event can make me think twice about where I am and what I'm saying. 

Some workplace dress codes exist to protect their employees' bodies. If you are a fry cook or a construction worker, it is incredibly dangerous to wear open-toed shoes on the job. You can get seriously injured if you're wearing shorts while dealing with hot grease. Not all entry-level fast food employees are smart enough to know intuitively that you can't wear jean shorts and flip flops to work. Sometimes, you need to tell them, on their first day of work, exactly what the dress code expectations are.