The witness told Preston Crown Court that the MP "put his arms all over me and tried to kiss me". He pulled away and left the room "as quickly as possible", he said.
The witness is one of seven young men that Evans, 56, is said to have assaulted.
The Westminster worker said he did not report the alleged incident at the time because he gave "the benefit of the doubt" to the defendant, who he considered "one of the nice guys".
But he said he came forward to the police following the reporting of Evans's initial arrest last year.
The incident is said to have taken place in February 2011 when the MP invited him, a friend and others to join him for champagne in his offices. During the evening, the alleged victim said he was invited by Evans to look at a nearby newly-fitted kitchen, the court heard.
He said the Ribble Valley MP opened the door and then pushed him into the room.
The complainant said: "It was pitch black and then very quickly he kind of came forward and put his arms all over me and tried to kiss me.
"I remember him saying something like 'you're gorgeous'." He said he "gathered his senses" and pushed him off and left the room.
He told a number of people about the alleged incident but did not make an official complaint.
The court heard Evans sent the complainant a Facebook message several days after the kitchen incident. The MP wrote: "Hi (the alleged victim), my mobile number is ...., great to see you the other day." The young man responded: "Hi. Thanks for allowing us to gatecrash your drinks. We (he and his friend) both had fun." Evans then replied: "Yep, great fun!"
Referring to the message, the complainant told the court: "I kind of took it as him thinking 'do I need to worry about this incident being reported?'"
Evans denies one rape, two indecent assaults and six sexual assaults. The trial continues.