In the mid-1980s, the late Aussie realist David Stove offered a prize of 300 dollars (Australian) to the person who isolated the worst argument, hatched by the mind of a philosopher. However, the prize money was never collected - because no submissions received by Stove trumped his candidate for the worst argument, namely Kant's beauty that: "we cannot know things as they are in themselves.". http://www.maths.unsw.edu.au/~jim/stoveworstargt.pdf
A COMPETITION TO FIND THE WORST ARGUMENT IN THE WORLD
I know of an argument which, although it is almost-unbelievably bad, has not only escaped criticism by philosophers, but has received the endorsement of countless philosophers. I think it is the worst argument in the world. But I may be wrong: I therefore seek to learn of some argument even worse, if there is one.
Ten candidate-arguments were submitted. All of them had some merit, and some of them were very interesting indeed. But none of them is worse than the argument I had in mind when I started the competition. Consequently none of them wins the prize.
Three dimensions, it will be recalled, entered into overall degree-of-badness as here understood: (a) the intrinsic awfulness of the argument; (b) its degree of acceptance among philosophers; (c) the degree to which it has escaped criticism.
The argument - really a family of arguments - which I had in mind as the worst, was the following:
"We can know things only as they are related to us under our forms of perception & understanding in so far as they fall under our conceptual schemes etc. So we cannot know things as they are in themselves."
If there is a worse argument than this, I am still to learn of it. This argument has imposed on countless philosophers, from Kant to the present hour, yet is very hard to beat for awfulness.  Certainly none of the arguments submitted for the competition was either clearly more awful, or more widely-accepted, than this one. I probably erred in implying, in the information-sheet, that the above argument has entirely escaped criticism, but it has certainly led a charmed life. 
Traditional and Modern Philosophy,
University of Sydney
1st January 1986
I propose that the worst argument ever churned-out by the mind of a philosopher is the extreme, anti-realist universal generalization - running that: since every proposition lacks an assertible ground; therefore, objective human knowledge is impossible.
If there were no assertible grounds available for any proposition, how could "1" have been asserted? Whoever generated "1" found and used grounds - such as those bound-up in reason, language and experience to generate it (which seems to explain the self-reference failure). If every proposition lacked an assertible ground, no one could assert: "Every proposition lacks an assertible ground.". "1" presupposes its own refutation.
Since these anti-realists wish to affirm the universal lack of assertible grounds, then let them do so without recourse to making weapons out of reason, language and experience - as accomplices in their murder of knowledge.
Should the universe contain no assertible grounds for propositions - one could not pose the question: "Does the universe contain no assertible grounds for propositions?". Merely forumlating this question answers itself in the negative. Human knowledge is possible.
There are a couple of other "arguments" - which should receive dis-honorable mention for the prize. However - since the "arguments" contain fallacies like equivocation and self-referential appeals to their owners as the ultimate scientific authorities, they're just out-gassings of uncouth and untidy minds.
(1) Rob L Norton redefined the Sexual Selection term "preference". Under his narrowed re-definition, he requires organisms to express verbal "preference declarations", have "planning" ability and "premeditate" - in order for them to exhibit biological mate preferences. Then, he emptily concludes that - since non-human organisms cannot express preference declarations, plan or premeditate, they lack biological mate preferences. (In the mating-systems of non-human, sexually reproducing species, preferences for reproductive traits displayed by members of the opposite sex are known via experiments to shift allele frequencies in these populations.)
(2) Post-Modernist Jerry demoted 400 years worth of physics into "mind-dependent" illusions, then he insisted that the fundamental, physical constants, G, h, c, etc., are not constant! His universal negation is easily refuted.