Stephanie O'Brien, 24, was staying in the city with three friends at a Holiday Inn Express when the zip on her skirt became stuck, the High Court in Glasgow was told.
She said two of her friends went for help and brought security guard Clive Carter to the room, who pulled at the zip and broke it.
Miss O'Brien said she then decided not to go out with her friends. She added that, while she was in the room alone, Mr Carter returned to her room holding a fire extinguisher.
The jury heard she felt "sick to the stomach" when she saw him, and that he had claimed she had phoned reception to report a fire.
Miss O'Brien, from Cumbria, was giving evidence at the trial of Mr Carter, 35, who is accused of committing a breach of the peace at the hotel on Stockwell Street, Glasgow, by pretending he was reacting to a report of a fire, entering her room uninvited and scaring her, on November 4, 2012.
Mr Carter, from Motherwell, North Lanarkshire, is also charged with murdering Khanokporn Satjawat at the Clyde Auditorium in Glasgow on November 12, 2012, by repeatedly striking her on the head and body with a fire extinguisher.
He has pled guilty to the culpable homicide of Miss Satjawat and has lodged a special defence of diminished responsibility, but the Crown did not accept this plea.
Miss O'Brien told the court that she and three friends came to Glasgow for an overnight stay on November 3, 2012.
She said they were socialising in one of their rooms and getting ready for a night out when it was discovered that the zip on her skirt was stuck. The jury heard her friends went to find someone to help with it and returned with Mr Carter.
Miss O'Brien said he ripped the zip and the skirt was damaged, after which she was not in the mood to go out.
The witness said she was scared that she was in the room on her own and had the TV on quietly.
Miss O'Brien said she heard someone quietly knocking at door and froze. She added: "I got out of bed and tiptoed to the door." She said she did not want whoever it was to know there was anyone in the room.
The jury were told she looked through the peephole.
She said: "I saw the man that had been up at the room previously holding a fire extinguisher."
She said: "I froze at the door, terrified. I wasn't going to open it but then I kept thinking in my head 'I am 23 I have got to open this door, he works for the hotel', so I opened the door a little bit."
She said Mr Carter told her she had phoned reception claiming there had been a fire in her room.
She said his comments were "a lot of rubbish" and that she was then even more scared. She said: "I thought 'I need to get out this room and not turn my back on him'."
The court heard she thought he would hit her with the fire extinguisher if she did.
Miss O'Brien said she came out of the room, with the door of the room open and Mr Carter went inside. She told officers: "I could hear him talking away to himself. I could heard him saying things like 'so you have not gone out with your friends' and he also said something about my skirt but I can't remember what'."
She told him her friends were returning, and added that as Mr Carter came towards her, she ran back into her room and locked the door. Asked how she felt she said: "Terrified."
She claimed she and her friends told bar staff what happened but were made to feel "silly" and did not lodge a formal complaint.
The court heard the police contacted her a couple of weeks later to interview her about the alleged incident after Mr Carter had been charged with murder.
Carter denies the charges and the trial continues.