A combination of "Bullshit" and "retard".
Person 1: Hey, did you know that plastic is made from dogs!!!
Person 2: Who told you?
Person 1: Our Teacher.
Person 2: Bulltard!!!
The opposite of a docile tard, a bull tard is person who is both retarded* and extremely aggressive. Often possesses "tard strength." This person would rather fight you than talk it out; would rather use violence than intellect; would rather use brute force than finesse.
*Does not necessarily have to be actually retarded...simple dumbasses can also be tards, and by extension, bull tards.
Friend: Dude, your little brother just threw his bowling ball halfway down the lane and put a dent in our lanes!
Me: Yeah, sorry...he's a bull tard. He breaks things.
An idiot who thinks that stock markets always rise.
The bulltards who bought Google's stock at $500, since it was such a great price after falling from $650, have hopefully learned something now that it's below $400.