Klitschko (left) is only Chisora's 15th professional opponent
Britain's Dereck Chisora dismissed Wladimir Klitschko as someone who has mainly fought "taxi drivers" before their world title fight on Saturday.
Chisora, 26, will challenge Klitschko, 34, for the Ukrainian's IBF and WBO heavyweight belts in Mannheim, Germany.
"It's time for you to have a proper fight," said Londoner Chisora.
"You are on the way down and I am on the way up. You've never boxed anyone like me. I am young, I move my feet, I am fast. I am a different heavyweight."
In response, Klitschko suggested Chisora was a better boxer than fellow Brit David Haye - because at least he turned up for fights.
"He is a very special man with pretty good skills, he is much underestimated," said Klitschko at a head-to-head news conference on Monday.
"As a boxer he's got pretty good skills, determination. He's a very busy fighter, so there will be a lot of action on Saturday.
"He's better than David Haye - he is as good at promoting himself but he even shows up for the fight. But as a person, he is horrible."
Klitschko was set to fight WBA champion Haye last year before the Englishman pulled out with a back injury and negotiations have repeatedly stalled since then.
Chisora is giving up 5½in (13.97cm) to the 6ft 6in (198cm) Klitschko and has had 14 fights (all wins) to Klitschko's 58 (55 wins, three defeats).
However, Chisora's trainer Don Charles rejected suggestions his fighter's chance had come too soon.
"How do you get experience?" said Charles. "By doing the task. He has got the style to do it."
But Klitschko's trainer Emanuel Steward said his man had been upset by Chisora's "disrespectful" pre-fight rhetoric and warned the challenger to expect "a much more aggressive Wladimir".
Chisora's last fight was a ninth-round stoppage of Norwich's Sam Sexton on 18 September, while Klitschko knocked out Nigeria's Sam Peter in the 10th round a week earlier. Chisora is 6-1 to win Saturday's fight.