Just got this awesome emblem and callsign. The callsign says "What The?" with two mustachio cats at either sides. Apparently the requirements are.. shoot an explosive through a wall and kill an enemy. xD I never thought I would replace my All pro callsign, but damn i just did. the All Pro was 2+headshots with 1 bullet.
easiest way to get it is with c4 and noob tube. shoot your (or their) C4 with the noob tube when you see them to make sure that kills them. i dont know how i got it, but i didnt do this. i must be some kinda boss :3
Easiest way to get it is to throw c4 near someone then throw the EMP grenade near them. Worked almost 1st time for me.