A man from Tyneside has admitted killing his friend while they were testing out a stab-proof vest.
David Baxter, 31, of Newcastle, changed his plea to guilty at the city's crown court, having previously denied manslaughter.
He now faces jail after the court heard 18-year-old Christopher Baker, from Seaham, in County Durham, suffered fatal stab wounds in April.
Baxter was remanded in custody pending a sentencing hearing next month.
At a previous hearing, the prosecution alleged the teenager's death in Seaham was not a tragic accident but had been caused by "stupidity".
However, the defence said it intended to argue it had been due to "horseplay".
The case had been listed for a trial next month but Baxter entered a new plea on Friday.
Judge David Hodson said: "Sentence in your case will be adjourned for the preparation of a pre-sentence report.
"All sentencing options are open, but you must appreciate a custodial sentence is the most likely outcome."