a juggernaught is an extremely obese female, often dressing in clothes for a much thinner woman such as miniskirts and tank tops.
the name is taken from the game Modern Warfare 2, where the juggernaughts are extremely large, tough and hard to kill, it is the same with these female juggernaughts, it is unadvisable to approach one, as they often ensnare young men.
steve: "oh shit look, a juggernaught"
pete: "fetch me my intervention"
matt: "dude...theres a juggernaught behind us..."
will: "pretend you have not noticed and DO NOT make eye contact!"