As much as everyone wants to believe this originated in the hip-hop industry, it actually originated from Twitch.tv. Where there is an emoji called "Kappa" that has been used since 2012 to express sarcasm, joking, or double meaning, due to the grin on the emoji. People on Twitch who wanted what they are saying to be taken seriously began to say "no Kappa", which turned into "No Kapp". Thus, prominent twitch celebrities and streamers such as T-pain and others began using it on the platform, where it most likely found its way to the music industry, and has since been popularized as "no cap", because no community outside of twitch knows what a kappa emote is.
Man I'm super thirsty right now, no cap.
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