The alleged victim said he met ex-BBC Norfolk broadcaster Michael Souter after starting a casual job at the corporation in Norwich.
The witness, who cannot be named for legal reasons, told Norwich Crown Court he began doing odd jobs at Mr Souter's home, where he claims he was abused.
Mr Souter, 60, of Loddon, Norfolk, denies 19 sex offences, including indecent assault, indecency with a child and serious sexual offences against seven boys aged between 11 and 16. The allegations date from between 1979 and 1999.
The witness's job, which lasted for about six months, involved helping DJs and sometimes travelling with them in a radio car.
He said: "I sometimes did odd jobs for Mike, like cleaning his car at his house.
"On one occasion he offered me and a friend a beer and we accepted - it was the first time I had drank alcohol. I felt dizzy and the room was spinning.
"I was feeling unwell and he took me upstairs to lie down.
"When I woke up, I was in a bit of a shock. My trousers were down and Mike had his hand on me.
"He said 'Calm down, it's all right, don't worry'."
Jurors heard the man left his job at the BBC soon after and never returned to Mr Souter's house.
He said he did not tell anybody about the abuse because, as a teenage boy, he did not want to be labelled as gay. He spoke about it when he was approached by police in 2011.
Originally from Scotland, Mr Souter has worked as a producer and presenter in radio since the mid-1970s.
The trial continues.