of course, that's not even close to the conventional meaning of "drop the mic", even though the phrase itself is certainly not old.....urban dictionary will usually have a very wide variety of "definitions" offered up by eager social media-types looking for their 15 minutes.....
A mic drop is the gesture of intentionally dropping one's microphone at the end of a performance or speech to signal triumph. Figuratively, it is an expression of triumph for a successful event and indicates a boastful attitude toward one's own performance.