More than just a definition, a friend is defined by his or her acts. Behavior is the key.
Slandering me is not friendly. Calling me just to check up on how I’m feeling is friendly.
Making light of my disability is not friendly. Bringing chocolate when I’m flaring is friendly.
Friends may argue, but they won’t call names. Friends may play jokes on each other, but they won’t play nasty tricks.
I think you get the picture.