Refers to having a pointless debate with somebody utterly ignorant of the subject matter, but standing on a dogmatic position that cannot be moved with any amount of education or logic, but who always proclaims victory.
Origin:
"Debating creationists on the topic of evolution is rather like trying to play chess with a pigeon; it knocks the pieces over, craps on the board, and flies back to its
flock to claim victory." --
Scott D. Weitzenhoffer (From an Amazon.com
book review)
Man, trying to explain to those moon landing deniers that the
Apollo program was real is like playing pigeon chess -- all they do is
knock the pieces over and crap on the board.