That is the opinion of Liverpool legend and Sky Sports pundit Jamie Carragher.
Bailly was given his marching orders by referee Lee Mason in the 79th minute at Old Trafford.
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The score was 4-1 to Manchester United at the time, with Ole Gunnar Solskjaer’s side easing towards a third successive win.
Ivory Coast international Bailly dangerously slid into Bournemouth winger Ryan Fraser with a scissor motion in the middle of the pitch.
And Mason had no hesitation in brandishing a straight red card to the 24-year-old.
Bailly now looks set to miss Manchester United’s next three domestic matches.
That includes the league visit to Newcastle on Wednesday, the FA Cup Third Round match against Reading on Saturday and the trip to Tottenham a week on Sunday.
And Carragher could not understand why the centre-back made the challenge.
“I mean what’s he thinking?” Carragher said.
“They’re winning the game 4-1, it’s on the halfway line.
“He’s flying in with a scissor challenge.
“When you go flying in like that, we now know when a player is out of control, endangering an opponent, you go to ground, every chance you’re going to be shown a red card.
“Absolutely brainless that from Bailly, considering the time of the game, the score.
“It’s not today, the game’s won. It’s more going forward and the games he will miss.”
United held onto the 4-1 lead to maintain Solskjaer’s 100 per cent start to his interim reign.
Paul Pogba was the star of the show with a second successive brace.