Finnbrain is the act of using your phone especially on the appsnapchat. This then triggers the person's brain to block out any surrounding aspects such as voices, noises and scenic changes.
Finnbrain is the act of using your phone to textgirls on call with friends this results in blocking out any contact from people except for the content on the phone. Therefore it is called finnbrain
He has finnbrain because he will not respond to me after I call out5times