You have to put up with a lot throughout life, from obstacles to drama to unpreventable circumstances. How you handle the situation and how it affects your future reveals the type of person you are. But there are some things that you should never have to put up with. (In no particular order because they are all unacceptable.)
1. People who don't give you respect
No matter who you are, where you come from, or what your values are, you deserve respect. You should not have to deal with people who won't even make the effort to get to know you or listen to you.
2. Discouragement of your goals, aspirations, etc.
Be true to yourself, follow what you want to do, and have your own hopes and dreams. If you don't have support from you friends or family, still strive to achieve your goals and do what makes you happy.
3. Insincere friends
You don't need to have a lot of friends to be happy or experience good friendship. Those "friends" who only talk to you when they need something, or never let you be your own person, or expects unreasonable things from you, or are never truly there for you, are not real friends. Cut those ties before they become too toxic.
4. Not getting the time of day
You deserve to be loved and thought of and attended to. If someone doesn't take the time to talk to you or see you, he/she does not deserve the time of day.
5. Unfair/biased treatment
We live in the 21st century. People should not be still letting race or gender or stereotypes get in the way of interactions or decisions in life. We should all be treated equally and fairly.
6. Doubt/Degradation from others
Anyone who puts you down or challenges your abilities and self-esteem is not worth your time. You should be able to be sure of yourself and speak your mind without worrying about others tearing you apart.
7. Consistent mistakes
Obviously it's okay to make mistakes and to forgive and move on. But if there are consistent bad signs that show no effort to change or improve, you should not have to put up with it. We are all human and deserve several chances in life, but there is a limit of forgiveness and brushing things off.
8. People telling you what you have to do
You have total control over yourself. You decide what you do or say. People don't have the right to impose their wants or beliefs on you. You are strong enough to say no and do what you want.
9. Peer pressure (specifically in college)
If you get an ultimatum, or people won't like you or be friends with you if you don't do something, then you should get yourself out of that situation. Everyone always says 'don't give into peer pressure', but it really is important to be in touch with your identity and know who your real friends are and what you really want.
10. Empty promises
Promises are commitments. People shouldn't take these things lightly. If you make a promise, follow through with it. Empty promises reveal a lack of integrity and trust. You should not have to rely on someone or be expecting something and get your hopes up.