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.
Pajama casual is a term used when working from home and preparing for a video conference. All business above the waist and your pajama pants down below.