Children and teens tend to respond to unexpected or incredible things by saying cap in order to reply fast to a friend. It is typical in computer game chat rooms, school group discussion rooms and social media commentaries. As an example, when a friend tells him/her that he/she completed all his/her homework in 10 minutes, someone can respond by saying that it is cap. No cap is also used by teens to signify honesty when it comes to talking about something personal or serious. It has become a colloquial expression, a fun thing to do, and conversations have become more expressive and relatable amongst their peer groups. Know more about
cap meaning
Source:
Radarro