Typically, though not always:
Someone who has a ton of empathy will be extremely modest if they are not insecure. If they are insecure, they will lift up friends’ achievements no matter how small. This can cause distress if the feelings or actions are not reciprocated.
Someone who feels inferior will focus on superficial things or small, nit-picking things against themselves while disregarding it in others. This is typically a defense mechanism, as they are afraid of being put down for focusing on larger things.
Someone who feels superior will focus on gigantic things with themselves, while nit-picking superficial and small issues with others as they disregard it in themselves.
Note: An inferiority complex is often a masked superiority complex, and the reverse is true for superiority.
Also, though these are typical everyone is different. And while seeming cumbersome, it is easy to forget that people with these self-destructive behaviors cannot control them and have gained these in defense of trauma, pain or mental illness.
Finally, what you can do to help:
Someone who is insecure needs to be reminded that these things do not matter. They are often sensitive to criticism as well as praise. They often have OCD behaviors, focusing with intense perfectionism towards simple things. Insecurity is a form of intense anxiety, and often cannot be mitigated without medication.
Someone with an inferiority complex is sensitive to rejection and criticism, likewise completely brushing aside praise. They sometimes act in extreme modesty with praise. Depressive and anxious, they feel attacked when criticized and end completely discouraged of all actions, acting in implosive, self-destructive behaviors like burning or destroying homework and creative works or injuring themselves if a mistake is made. They need to be made to accept praise and circumvent what they feel inferior to. Nearly all the time, this requires psychological intervention on part of a professional.
They may also “run away” from social contact when feeling inferior. Most regard this as “emo” behavior. However, on the chase they may end up extremely explosive, acting in anger against people. This can also be rewarding, as they are more likely to open up when in this state. They tend to regard friendships as wasted time spent on part of their friends. Also, misanthropy is common.
People with Superiority complexes are spiteful, hold grudges and are explosive. Rarely self-destructive, they often damage others in their free-floating hostility. They bully and put down others, regarding friendships like they are doing others a “favor.” When criticized, they go on the attack, nit=picking, harassing and harming others. They expect to be forgiven easily while rarely forgiving others.
Superiority complexes cannot be broken without trauma or professional assistance. Mitigation requires medication and breaking both the hidden inferiority complex as well as the superiority complex.
Finally, the best thing you can do to is be a friend. To stay by these people who are so used to rejection- no matter what the illness tosses in the way of a friendship- is the greatest thing you can do to help them.