John Leslie laughed as he grabbed a woman's breasts at a Christmas party, a court has heard.
The former Blue Peter presenter, 55, is accused of attacking the woman at a gathering in London's West End more than a decade ago.
He denies sexual assault by intentionally touching the woman without her consent on December 5, 2008.
Prosecutor Jocelyn Ledward told Southwark Crown Court on Monday: "The prosecution say this was no accidental touching, but a quite deliberate sexual assault.
"The defendant laughed again and then walked off as if what he had done was completely acceptable and was not something anyone was going to challenge him on."
The woman did not think her complaint would be taken seriously at the time but told a friend who was left "shocked", the court heard.
It was in late 2017, after the MeToo campaign became prominent, that she decided to come forward.
Leslie voluntarily attended a police interview in March 2018, at the end of which he said: "I have not attacked or assaulted anyone ever."
Leslie, whose full name is John Leslie Stott, sat in the dock wearing a grey suit, as the case against him was outlined.
Ms Ledward said he grabbed the woman's breasts "quite deliberately for a period of a few seconds" before walking off.
She said: "The woman was stunned but did not report it to the police. He (Leslie) denies he did any such thing, and if there was any physical contact between them, then it must have been an accident."
The woman had recognised Leslie at the bar and went over to him and he smiled at her, the court heard.
The prosecutor added: "She smiled back. Without saying anything further he grabbed both of her breasts with both of his hands and laughed as he did so."
This went on for about three seconds, the court heard.
The trial opened on Monday but the jury was discharged in the afternoon, and judge Deborah Taylor said the case would start afresh on Tuesday.
She told the jury: "A juror is unable to carry on so what I am going to do is, since we are in the early stages (of this case), is to discharge this jury and swear in another."
Leslie, from Edinburgh, appeared on Blue Peter between 1989 and 1994 and also presented Wheel Of Fortune and This Morning.