The invective came as Pyongyang said it could see no justification for talks with Washington on Monday.
Six-party working level talks on the communist North's nuclear weapon ambitions had been planned for August but have yet to begin.
The date for more senior talks is also in question, although diplomats note Pyongyang often raises its rhetorical voice before attending talks or compromising.
In a strongly worded statement published by the official KCNA news agency, a North Korean Foreign Ministry spokesman said Bush had hurled "malignant slanders and calumnies" against Pyongyang's leadership under Kim Jong-il.
"This clearly proves that the DPRK [Democratic People's Republic of Korea] was quite right when it commented that he is a political imbecile bereft of even elementary morality as a human being and a bad guy, much less being a politician," the spokesman said.
"Bush is a tyrant that puts Hitler into the shade."
The spokesman said it had been impossible to hold working level talks between the two Koreas, China, Japan, Russia and the US because of hostile American policy.
"This made it quite impossible for the DPRK to go to the talks and deprived it of any elementary justification to sit at the negotiating table with the US," he said.
However, a South Korean official said the North was not unequivocally ruling out talks and noted there were still five weeks until the end of September, by which time full six-way talks are supposed to have been held.