The Dutchman was so unhappy with what he perceived to be simulation by Alexis Sanchez that he dropped on to his back in a mock demonstration of what he had seen.
Louis van Gaal accused Alexis Sanchez of diving during Manchester United's match against Arsenal on Sunday by mockingly falling over in front of fourth official Mike Dean.
The Dutchman drew huge cheers from the Old Trafford crowd when, after an argument with Dean, he suddenly collapsed on to his back in an apparent demonstration of what he had seen.