Most is a smelly jockstrap. It derives the early days of baseball when players would wear the same jockstrap the whole season. At the end of the season they would make the rookie players smell them and wear them around their heads in a form of hazing. Though it was frowned upon, it occured quite frequently. The word "most" was used because of the high stench the jockstrap gave off.
"Hey you stupid rookie bitch, smell my most!"
"Take this most and strap it to your forehead you fucking bitch!"