Mark Byrne (44) told the Herald that his family have been left traumatised by the horrific robbery.
"The guards told us he could have been prepared to use the knife to get what he wanted," he said.
Four members of the family were at home after spending an enjoyable Christmas Day when the thief put a tool through the letterbox and managed to open the door.
Mark, his wife Greta and daughter Sophia (16) were in their beds upstairs at 1.30am on December 26 when the armed thief entered. However, his son Luke (18) was still awake in a back room.
"Luke saw a shadow in a mirror and jumped up when he saw him. But the guy had a carving knife and threatened to stab him," said Mr Byrne.
"He told Luke something like 'Get back or I'll stab ya!' Luke is six foot two and the fella seemed fairly scrawny but he had a knife. I heard Luke shout loudly and we all went running down the stairs. But he had grabbed my wife's handbag from the sofa and had run out through the front door before we got to the bottom of the stairs," he said.
"It was all over in 10 seconds," he said.
"It's terrible. It was an invasion of our home," said Mr Byrne, who lives in the Monastery Gate estate in Clondalkin.
"He must have been looking for cash for drugs. He didn't care if he was recognised. He didn't wear a mask or gloves. He could see we were at home as the car was parked outside and we have a house alarm. There was even a picture of our [boxer] dog beside the front door on a sign that says 'I live here'.
The thief appeared to be in his mid-20s with tightcut black hair. He wore a grey hoodie and had a Dublin accent.
"There was money in my wife's handbag but it also had sentimental items, including family memorial cards," he said.
"It ruined our Christmas. I lived here for 15 years with no problems then twice in the last few months we've been victims of crime.
"My car was parked near the dog park at Corkagh Park when it was broken into and the sat nav was stolen. Now this," he added.
"The guards have advised us to make sure to lock our front door from the inside otherwise thieves can use a tool through the letterbox to turn down the door handle on the inside.
"The guards have been very good but we need more of them. We're told the crime statistics are going down but that's no good if you suffer from crime yourself.
"We heard there were a couple of other break-ins in the area the same night," he added.