To run upwards on an escalator going the opposite direction. In other words, running upwards against an escalator headed down. Typically, dropboxing is done on extended escalators such as those found in many large US cities, such as the ones providing access to the Washington, D.C. metro rail.
Jim and Tony were really sore after a late night out ended with the two dropboxing the Chinatown metro to impress Kathy and Diane.
A small piece of information. Derived from the word ken, used often in the scottish language and is synonymous with knowledge.
Person 1: "Hey I don't get this shit. How do you solve this problem?"
Person 2: "I got that one. Give me some kenlets on this assignment and I'll help you w/ that one."