(exclamatory phrase) a playful indication of surprise, misfortune, or insult
popularized by Tracy Morgan of Saturday Night Live, OH SNAP is seemingly derivative of oh no you didn't where an insulted person, for example a guest of Jerry Springer or often a spunky African American woman contends the insult being made against him/her. While derivative of "oh no you di-int," OH SNAP has more of an emphasis on playfulness and can be said by people other than those being insulted.
(exclamatory phrase) a playful attempt at indimidation which follows an insult
popularized by DT, OH ZIP is derivative of OH SNAP where an insult is followed up by this indication of surprise. While derivative of "oh snap" OH ZIP has more of an emphasis on intimidation and plays off the implication that the speaker is unzipping his pants to reveal an larger-than-normal appendage.