But Koskinen kept his cool.
Rep. Michael Turner, a Ohio Republican, tried to push Koskinen to say whether a crime had been committed amid the IRS scandal.
Turner pushed back after Koskinen said he had not seen any evidence of a crime or any evidence for any number of other things relating to the lost emails belonging to former top IRS official Lois Lerner.
"We have no evidence whether she (Lerner) beat her dog, whether she beat children," Koskinen said.
But then Turner questioned Koskinen's integrity when he said he would not call the FBI to investigate the agency.
"I reject the suggestion that my integrity depends on my calling the FBI," Koskinen said, and later said there were "no facts" behind Turner's criminal accusations.
He later said he hadn't seen any evidence of "wrongdoing" in the loss of Lerner's emails, triggering more Republican incredulity.