I haven't made many friends in my life so far, but, as a general guideline:
1. Somebody who really takes time to listen and understand what I am thinking and feeling, somebody who takes my views and concerns seriously, rather than mocking them right away. It would be best if we agree on a number of key issues that I feel strongly about.
2. Somebody who's perhaps more expressive than me, because I'm not always that good at expressing my feelings.
3. Somebody who can appreciate the fact that though I may still be relatively young, I have things I strongly feel about and I often feel out of place with my peers or slightly older people. Growing up, I often preferred the company of adults rather than other kids, and was labeled as anti-social by some teachers (note, not the personality disorder). 'You are still young', 'act more like your age, have some fun and be more outgoing' are some of the quickest ways to make me withdraw and not want to engage you any further. I consider myself an old soul in many ways.
4. Someone who is loyal and dependable out of a deep and mutual trust and desire to be in each other's lives.
5. Somebody who knows and believes in my best qualities, but also knows my weak spots. Somebody who doesn't force me to change my fundamental self.
6. Somebody who's a bit more practical and grounded when necessary, or rather, when there's no other choice but to push forward and get something done.
7. Somebody who's kind, gentle, and caring, who has compassion for the weak and helpless rather than contempt.
8. Somebody who is authentic to themselves without feeling the need to be anything they are not. Somebody who is not afraid to challenge conventions and expectations, as long as it's still in-line with my values and beliefs.
9. Somebody who can appreciate the need for quiet time and for relative silence, without feeling 'bored' or 'off'. Somebody whom I can enjoy my time and feel at ease with even when there's no plan, no structure, no deliberation, nothing.
10. Somebody who desires nothing but a quiet, peaceful, and happy life.
Of course it's rare, if not impossible to find someone who matches all 10 of these criterion, and I'm a bit more flexible than I may appear to be in writing this, but the absolute nightmares for me would be:
1. Being forced to change my fundamental self into something I don't agree and am not comfortable with.
2. Being with someone who lacks fundamental kindness and goodness.
3. Being dismissed for how I feel and what I need to share because I view he / she as someone close to me.
4. Disagreeing over key issues and values. (EX: I am completely against corporal punishment on children, but he / she fully supports it).
If these lines are crossed, I will find it extremely difficult to feel anything good in my relationship with that other person.