A Dreadsock is a standard sock with a (metal) 40K Dreadnought inside. The Dreadsock is then used to 'beat the stupid/cheeze/beard/shit' out of people.
In general useage, "Dreadsock" is usually suggested to emphasise how stupid a situation is.
Note: it is not advisable to actually hit someone with a real Dreadsock - it can cause serious injury, and get you in a lot of trouble!
"This guy at my local club insists on using illegal rules combos and claiming it's legal! We've tried time and again to make him learn the proper rules! How do I get through to him?"
"Take one Dreadsock, and apply as many times as needed to make him stop."