We can considered a person who is not good with our mental health if that person causes you anxiety and always put you in difficult situation. Dealing with them can be draining.

I listed some traits of those persons to familiarize yourself with and help you deal with these trying relationship.
1.  Toxic people tend to manipulate person for their own benefit. They use other people to get what they want. They don't sympathize the need of the people their using.
2. They are bad critics. They criticize everything about you, what you've done and what you didn't do. They don't take criticism and often lie if serves them.
3. They take no responsibility for hurting other feelings, rather their feeling are projected onto you. If you try to point out this to them. they will defend their perspective and take no responsibility or almost anything they do. They don't apologize, but try to gain sympathy and attention by claiming "victim" status.
4. They knew you when they want something from you. They are inconsistent, they may change their attitude instantly depending on what they feel they need to accomplish. They know how to be kind when they want something from you.
5. They want your loyalty and you have to prove it to them. They pushes you to choose them over something else or something you want, even to the point to cut off other meaningful relationship to satisfy them.
6. They don't appreciate what is important to you. They are not caring and supportive. They don't like you to grow or to succeed because you move the attention away from them and thwart them from focusing on their own goals.

Surrounded with toxic people you have known always leaves you emotionally drained because you always end up fixing their own problems which always make you feel frustrated and unfulfilled. 
Don't allow yourself to become depleted because of give and give but no return relationship.  You also have your own life save your time and energy. 
  If you think you likely have those kind of relationship, it's time to sit down and assess your situation. They may not change but you can. Weight the pros and cons, make a decision to limit your time with this person or end the relationship.
 "Life is a one time offer spend it with good people and not with people who are not good for your mental health."