Jason Nelson, 32, admits killing Jordan Maguire, 20, at his Luton home, in a "spree of violence" on 26 May 2013 but claims it was done in self-defence.
The former resident of Marsh Farm Estate in Luton has pleaded not guilty to murder, rape and sexual assault.
A man who saw Mr Maguire stabbed three times said the accused "showed no regrets or remorse" afterwards.
Luton Crown Court heard the attacks happened at Mr Maguire's home in Thrales Close between 18:00 and 20:15.
The prosecution allege Mr Nelson was in the middle of a spree of violence, having sexually assaulted a 25-year-old woman in the stairway of some flats and then a 60-year-old woman in her flat.
Witness Dennis Kamau said he and his girlfriend were looking to buy some cannabis when he came across Mr Nelson near the Nisa store on the estate.
He took the pair to Mr Maguire's home where the men entered the house while the woman stayed outside.
After the pair agreed to share a deal, they went to the kitchen where Mr Maguire removed a tin from a kitchen cabinet.
Mr Kamau said: "The next thing I saw was a knife rise above and attack Jordan.
"I saw the knife go into Jordan. Jordan acted all shocked. He stabbed him a second time."
Mr Kamau told the jury the victim was then stabbed in the back by Mr Nelson who said "You little pussy" before putting the knife away and riding off on his bike.
"I was scared, terrified and shocked," said Mr Kamau.
Asked how the accused appeared, he said: "He showed no regrets or remorse."
A stab wound to the chest had punctured Mr Maguire's aorta and he was fatally injured.
The jury earlier heard Mr Nelson stayed for two weeks with a girlfriend in Ipswich before flying to his native Grenada and was later arrested in Trinidad.
A man who stabbed a drug dealer to death showed no remorse after the knife went in, a jury has heard.