Scores of supporters left the ground in the second half and former United midfielder Paul Scholes said the players and manager looked "bored" during the match.
Speaking to reporters ahead of Tuesday's Premier League clash with Newcastle United, Van Gaal admitted he had also found some of his team's performances tedious.
"There are matches that I have enjoyed very much. Against Chelsea (last month) I have enjoyed it, but the result was 0-0 and we could have lost also," he said.
"There are also matches where I'm very bored or angry because we are not disorganising our opponent's defence, but that is football."
United are fifth in the Premier League standings and have won their last two matches following a run of eight games without victory.
The team have been criticised for a dull style of play that is at odds with the club's attacking traditions.
Failure to beat third-from-bottom Newcastle will rekindle the scrutiny on Van Gaal, especially after the manager acknowledged the fans' frustration with his side's laboured displays.
"They have been ironic (against Sheffield United) but that's an expression of the fans and that's good. The players were frustrated and the fans were frustrated.
"But the fans also have to know we can't always play fantastic football and that was also the case in former days when it didn't happen. I'm sorry about that, but it is like that," he added.
(Reporting by Simon Jennings in Bengaluru; editing by Amlan Chakraborty)
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