You've heard it your whole life: "Stand up for yourself." But it's much easier said than done – especially for new employees in unfamiliar work settings. You might not know where to draw the line, or whether things have truly gone too far, or if you even deserve to "stand up for yourself." But there are a few situations in which you absolutely should – because after all, according to Margie Warrell on Forbes, it's your job to teach people how to treat you.

1. Your boss is ignoring the "TO" in "PTO."

In my first news reporting job, I once found myself out on a sick day, stuck on my living room couch shivering and sweating with a fever. My phone rang, and it was my editor, telling me to do a follow-up phone interview that very minute for a story I'd submitted the previous day. It was my first job out of college, and I was so grateful to even have it. I didn't see standing up to my boss as an actual option. So I powered through and did the interview – and ended up working from home for the next several hours, flu symptoms notwithstanding.

Many first-time employees wind up in a similar situation sooner or later, and here's the truth about it (even if it doesn't feel true in the moment): If you are taking paid time off, you have the right not to work. If you're out sick or on vacation, that's your time, not your boss's. If someone asks you to work during a sick or vacation day, put your foot down, either by negotiating additional PTO or asking your boss to delegate the tasks to someone else.

2. Your coworkers are making you uncomfortable.

It's important to feel safe and productive in your work environment, and if coworkers are killing your vibe, it may warrant action. If people in your work space are being rude to you, don't be afraid to call them out – but do so strategically. While being passive in such situations is unlikely to help you, acting aggressively probably won't, either. It's important to find that space between passive and aggressive – be assertive, Psychology Today reports.

The best way to act assertively without coming off as aggressive or self-righteous is by putting yourself in the other person's shoes. Imagine your coworkers' thoughts and feelings, and take those into account when you take your stance. Double-check how you can clarify your perspective on the situation without attacking other people involved, while also reminding yourself that your feelings are valid.

If asserting yourself proves ineffective, take the matter to your superior, again keeping in mind that while you want to act assertively, you don't want to seem aggressive. And if your coworkers are making you uncomfortable with violent or sexually inappropriate behavior, involve your boss or HR rep immediately to ensure your protection.

3. Your employer isn't respecting your time.

No job is perfect. You may at times find yourself staying late in the office to complete all your tasks, or help your boss and colleagues complete theirs. However, if this becomes a regular occurrence and your employer is taking clear advantage of your time, consider speaking up. Arrange an intentional, in-person meeting with your boss to discuss boundaries regarding your work schedule. Of course, this meeting might seem scary, but it's necessary – unless you're willing to give up your personal life for your job.

Taking a stand in seemingly small-potatoes situations like this might give you more clout in the long run, as well. Social psychologist Adam Galinsky wrote in a TED blog post that each of us has a "range" of behavior in social situations (including the workplace), and that range depends on how much power we have. For example, the more powerful you are in your work space, the more leeway you have in how to behave. On the other hand, if you feel pretty low on the totem pole, you may assign yourself a small range of permissible behavior.

If clarifying work hour boundaries feels out of range for you, find ways to empower yourself so you feel more comfortable speaking up. You might do this by asking for advice from and advocating for your colleagues, creating more social support for you in the workplace. Another method is by signaling flexibility: When you meet with your boss, present a variety of solution options, rather than just demanding one fixed solution. For example, if it's impossible to stick to one set work schedule, perhaps your employer would be willing to comp your overtime hours during less busy periods.

4. Your skills are going to waste.

Perhaps you were hired with the explicit expectation that you would be out in the field, working with others, when in reality you spend most of your time crunching numbers alone at a desk. In such situations, you might feel like you're not exercising your most marketable skills, and you're losing those skills when you don't have opportunities to practice them. This is another situation that calls for you to expand your range and ask for change. Sit down with your employer to discuss why you aren't being trusted with the type of work you expected to tackle in your position, and how you and your boss can work together to change that.

Again, these conversations might seem intimidating, but in the long run, they create a win-win situation. You'll feel happiest and most fulfilled doing work that employs as much of your skill set and potential as possible, and your company will ultimately benefit as a result.