Personally, I have never actually witnessed someone quitting out of a public match yet for not getting a shovel, but if it DID happen, I would message them telling them how much of a pathetic little baby they are, then mark them as an avoided player and move on from it.
Box humpers are just greedy morons who know nothing about how to play the game properly, and if I am in a game with someone who does it before getting jugg, I try telling them how stupid they are being. All this over the Mark II!?! You get a single burst Mark II handed to you at the very beginning of the game in the Mauser.
Either way, if you are on XBOX, just mark the players as avoided and move on from it. You will barely ever see those users online again.