how to be mean?

You just have to learn to say no and set limits. You don’t have to learn to be mean (that would go against your nature and it wouldn’t be true to yourself) but you do need to learn to be firm and say what you think or feel. I say this because I’ve been in exactly the same situation! And when you say you’re being taken advantage of, see it as you are letting someone take advantage of you and this is where you have to learn to say “sorry I can’t help this time” or “no, I’m too tired”. When I started doing this it was difficult at first (mostly because I wasn’t used to saying no and it made me feel guilty) but then it got easier and I realized I wasn’t doing anybody a favor by being too nice (lastly myself). setting limits is good for you and it let’s people know that they also have to respect those limits and not always count on you to do everything for them. Don’t be scared to stand up for yourself and say what you think or feel. It’s not about being mean or nice but about being true to your needs. You can’t help anyone if you don’t help yourself first.