Van Gaal has reportedly been given two games to save his job after United's miserable six-match winless run cost his side their place in the Champions League and saw them drop out of the Premier League's top four.
Rumours have been rife this week that the former Barcelona and Bayern Munich boss is about to be sacked and replaced by Jose Mourinho, who was dismissed by Chelsea last Thursday.
Quizzed about the speculation by reporters at his weekly press conference ahead of Saturday's trip to Stoke, Van Gaal quickly became irritated and it was less than five minutes before he decided he had had enough.
Lack of unity pushes Van Gaal to the brink
Refusing to take any more questions, the Dutchman walked out, saying as he passed a table of mince pies and wine that had been laid on for the media: "I wish you a merry Christmas and also maybe a happy new year when I see you.
"Enjoy the wine and a mince pie. Goodbye."
Van Gaal, who has overseen just three victories in United's last 13 games in all competitions, only answered three questions from the broadcast media and then refused to take any questions from the written press.
It was clear the 64-year-old was in an angry mood from the moment he took his seat in the media room at the club's Carrington training ground.
Van Gaal acknowledges Man Utd pressure
"Has anybody in this room not a feeling to apologise to me? That's what I'm wondering," he snapped after being asked about (Arsenal manager) Arsene Wenger's claim Van Gaal's treatment had been "disrespectful".
Van Gaal, under intense pressure since last Saturday's 2-1 Premier League defeat at home to Norwich, said he has received calls of support from former United manager Alex Ferguson, as well as former chief executive David Gill and current executive vice-chairman Ed Woodward.
Despite that backing he is widely expected to be dismissed by owners the Glazer family if United lose at Stoke on Boxing Day or at home to Chelsea on Monday, yet Van Gaal feels that he has been treated unfairly by the media.
"I think I was already sacked, I read I have been sacked. My colleague (Jose Mourinho) was here already," he said.
"What do you think happens with my wife or my kids? Or with my grandchildren? Or with the fans of Manchester United? Or my friends? What do you think?
"They have called me a lot of times and also Arsene Wenger is saying something about that.
"So you think that I want to talk with the media now? I am here only because of the Premier League rules. I have to talk with you.
"But I can only see when I say something that you use my words in your context. And I want to say only that I have tried to lift the confidence of my players."
Van Gaal gave a speech to his squad at the players' Christmas lunch on Monday, urging them to show unity as they attempt to improve their form while enduring criticism from former United players, the club's fans and the media.
"I have done everything this week. I held meetings with the players with my members of staff, I hold a Christmas lunch, I did a speech and I feel the warmth and support of everybody in Carrington, at this training complex," he added.
"But I didn't feel that in the media and of course I can imagine that you can write about that subject.
"We are not in a good position but four weeks ago we were first in the Premier League and in four weeks' time we can be back in that position again.
"I have received calls from Alex Ferguson and David Gill and Ed Woodward because you are creating something that is not good, what is not being the facts."
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ