The enigmatic referee sent off Sofiane Feghouli in the first half, and missed Zlatan Ibrahimovic’s offside goal that doubled Manchester United’s lead.
But this clip is also doing the rounds on Twitter of him talking to Pedro Obiang after Sofiane Feghouli’s red card.
Lip readers suggest that the referee told the Spaniard: “Don’t look at me again, otherwise you won’t be playing again.”
Hammers players were incensed with the decision to dismiss Feghouli after a late challenge on Phil Jones.
The Algerian’s feet were on the ground while Jones came in over the top to win the ball and was criticised for his dramatic reaction to the challenge.
In a Sun poll, 79 per cent of readers said Dean had got the decision wrong.
And Gary Neville commented: “Think of the red card two-footed sending off we have seen – it’s not one of those.
“It’s a poor decision and the West Ham fans are letting Mike Dean know.”
Dean and his team further infuriated the Hammers in the second half when he failed to spot Zlatan Ibrahimovic scoring United’s second from a clear offside position.
Jose Mourinho’s side could have scored another offside goal in the first half when Antonio Valencia hit a tap in straight at Darren Randolph and Jesse Lingard fired an even simpler rebound against the post.