A terrified teenager summoned help through Facebook while barricaded in the bathroom away from her boyfriend she thought was about to kill her.
Joshua Knight had warned his victim "I don't want to hurt you but I''m going to hurt you" and later pointed a gun, which she believed was real, at her during a "horrifying" confrontation.
The 19-year-old "snapped" after inviting his girlfriend to spend the night at his Sunderland home while his parents were away last summer, Newcastle Crown Court was told.
After barricading herself in the bathroom for safety, the 18-year-old victim sent a plea for help through a Facebook chat group she had with friends, saying she was about to be shot and possibly killed, then included a picture of her own terrified face.
While she was issuing her desperate plea, Knight was banging on the bathroom door threatening to kill her.
As a result of her desperate request, the police were contacted and Knight, who has been offered a university place and had no previous criminal record, was arrested.
Police found a collection of weapons including the gun, two hammers, a kitchen knife and a baseball bat outside the bathroom door.
The victim was "hysterical, absolutely terrified, suffering from shock" when officers got there, the court heard.
The weapon was a BB gun, which Knight had for cosplay conventions - and he admitted having it with the intention of causing fear of violence that night.
Judge Stephen Earl told Knight his behaviour was "bizarre" and added: "The fear that felt by your then partner in relation to that evening in question must have been horrifying."
Knight, of Lonsdale Road, Sunderland, was sentenced to 16 months imprisonment, suspended for two years, with rehabilitation requirements, £800 costs and a restraining order to keep away from his now ex-girlfriend.
The court heard the teen had never been in trouble before, and experts concluded his behaviour on the night could be linked to autism spectrum disorder.
He has been assessed as posing a low risk of violence and is now in receipt of professional help with the support of his family firmly behind him.
In a series of references from respected members of the community, as well as his own parents, Knight was described as a "kind and gentle" character with a history of good, respectful behaviour.
His own father described him as "the perfect son" with a family who are all proud of him.
Anne Richardson, prosecuting, said it was after the couple had been drinking and watching a film at Knight's home his behaviour began to change, and he made the sinister threat about hurting her.
When he went upstairs the woman followed a short time later, to check if he was all right.
Miss Richardson said: "She got to the top of the stairs. He was about two metres away, with what she thought was a gun.
"She thought it was real and it was pointing at her.
"She ran into the bathroom and locked the door. She dragged shelving against the door to barricade herself in.
"He started banging, saying is she came out he was gong to kill her."
The court heard the victim was so scared she started vomiting in the bathroom before turning to social media for help.
By then Knight was warning her not come out of the bathroom, even if he told her to.
Miss Richardson continued: "She went on Facebook and began group chat with three of her friends.
"It is clear from the messages she believed she was going to be shot, possibly die.
"There is a photo of her with her hand over her mouth in the bathroom.
"All the while, he continued to shout and bang on the door.
"Shortly after, she received a message from the group saying the police were on their way."