Giving evidence at the defamation trial of highly decorated special forces veteran Ben Roberts-Smith, the soldier said the leg helped him decompress while on tour.
"It helped me decompress. Let off steam. Bond," the witness, codenamed Person 14, told the Federal Court on Tuesday.
"(It's) high tempo life, high pace, you never know when your last day is coming."
Images of soldiers drinking from the leg at the SAS's unofficial bar in Afghanistan, the Fat Lady's Arms, caused controversy when they emerged in 2020.
The leg came from an insurgent shot dead in a compound known as Whiskey 108 in 2009, the court has been told.
But the manner of the shooting is disputed, with Mr Roberts-Smith, a Victoria Cross recipient with six Afghan tours under his belt, saying the man was fighting age and armed with a rifle.
The three newspapers the war hero is suing for defamation say the man was in fact a unarmed "person under control" who was thrown to the ground and executed.
A soldier codenamed Person Six took the prosthetic leg back to the Australian base. It was later transported to the SAS's Perth barracks and mounted on a wall and small glass replicas were presented to some soldiers.
Person 14 denied he was comfortable drinking from the leg because he knew it had been removed from an insurgent.
While accepting the Whiskey 108 mission was significant historically and had resulted in no casualties, he said he never saw the leg as a trophy in which the unit had pride.
Earlier, the witness clarified evidence given on Friday, placing Mr Roberts-Smith out of earshot when his SAS patrol commander spoke of the need to "blood the rookie" during the same 2009 tour.
Person 14 had said Mr Roberts-Smith was "present" in a large room of the Australian base in Tarin Kowt in 2009.
That led to an accusation by the Victoria Cross recipient's lawyer that the witness had lied to the Federal Court.
"You've come here to throw Mr Roberts-Smith under the bus in any way you can, haven't you?" Arthur Moses SC said.
"No, he was present in the room, but not present in the circle we were in," Person 14 replied.
"When you said ... that Mr Roberts-Smith was present, he wasn't present, was he?" Mr Moses continued.
"He was in the room but he was not part of that. He was present but not for that conversation," the witness said.
The phrase references a junior soldier getting their first kill in action, and allegedly led to Mr Roberts-Smith being complicit and responsible for the shooting of an unarmed, non-threatening man by a rookie soldier at Whiskey 108.
That allegation is a key incident described in three newspapers' reports about Mr Roberts-Smith, which the war hero is now suing over.
The 43-year-old former soldier has denied allegations of war crimes and murders, claiming such reports in The Age, The Sydney Morning Herald and The Canberra Times in 2018 unlawfully defamed him.
The newspapers, pleading a truth defence, say the 2009 tour involved Mr Roberts-Smith and his patrol commander, codenamed Person Five, making statements at various times about their need to "blood the rookie".
Person 14 denied hearing Mr Roberts-Smith utter the phrase.
The hearing resumes on Wednesday.
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