The TV presenter was responding to questions about his public persona while giving evidence for a second day at London's Southwark Crown Court.
It came as Mr Harris, 84, revealed how he admired a 13-year-old friend of his daughter sexually while on holiday.
Sasha Wass, QC - who also said before jurors that he was a "polished performer" - asked the Australian star whether he was good at hiding the dark side of his character.
He replied "Yes" before the QC said the trial would need to fathom "how dark that dark side actually is".
The issue was raised as Mr Harris said his wife and daughter had not known of his relationship with an alleged victim.
He was speaking about a childhood friend of his daughter who is the subject of seven of the 12 indecent charges he faces. He claims to have had a consensual relationship with her when she was an adult, but that nothing happened while she was a child.
When he said friends and family had not known about the relationship, Ms Wass asked: "You are pretty good at disguising that dark side of your character, aren't you?"
"Yes," Mr Harris replied.
Mr Harris also told jurors of his sexual interest in the 13-year-old friend. He conceded that when he complimented the teenager on her bikini during the holiday in the 1970s, he was actually referring to her body.
Mr Harris, of Bray, Berkshire, is accused of 12 counts of indecent assault on four alleged victims between 1968 and 1986, all of which he denies.
Seven relate to the friend of his daughter, who claims he abused her from the age of 13.
Mr Harris, who was supported in the public gallery by wife Alwen and other family members, sat in the witness box as he admitted that he might have complimented the girl's bikini on holiday when she was 13.
Ms Wass put to him that bringing attention to her bikini was actually a comment on her body, and suggested he was admiring her sexually.
She asked: "Do you accept that when a man tells a woman or a girl that they look lovely in a bikini, they are not actually admiring the clothing, but they are admiring the person's body?"
Mr Harris replied: "Possibly."
Ms Wass asked: "What you were saying to (the alleged victim) is 'You have got a great body'."
Mr Harris said: "I suppose so."
The QC added: "When she was 13?"
Mr Harris answered: "Yes."
Ms Wass said: "And you made it plain to (the alleged victim) on that holiday that you did admire her, admire her body?"
Mr Harris answered: "On one occasion, possibly."
The prosecutor added: "And you admired her sexually, that's what that is."
Mr Harris answered: "It did not compute to that in my mind... in hindsight, I suppose it is."
Ms Wass went on: "It seems from where we are going from your answers to the questions that you admired [the alleged victim's] body sexually during that holiday."
Mr Harris replied: "It's possible, yes."
The prosecutor added: "And, of course, once we work out that you did see [the alleged victim] in a sexual light during that holiday, everything that [she] says becomes realistic, doesn't it?"
Mr Harris replied: "Not as far as I'm concerned, because it never happened." He firmly denied Ms Wass's claims he played with the alleged victim "like a toy".
Mr Harris described his guilt at "betraying everyone" with the affair. He has also admitted a second affair with a woman who lived rent-free at his home.
But Ms Wass said the sexual encounters with his daughter's friend were not consensual, adding: "This was child abuse." The trial continues.