The boss admitted to being “fed up” with talking about “dubious” penalty decisions, after United were awarded a spot-kick in the third straight match against his team when Douglas Luiz was adjudged to have fouled Paul Pogba.
Bruno Fernandes scored from the spot to cancel out Bertrand Traore’s first half opener for Villa, with goals from Mason Greenwood and Edinson Cavani earning a 3-1 win for the visitors which meant Manchester City must wait to seal the Premier League title.
Smith’s mood got no better when Ollie Watkins was then sent-off, after receiving a second yellow card for what referee Chris Kavanagh deemed to be a dive. The striker, who hadn't missed a minute of the season, is out of Thursday’s match with Everton.
Smith said: “The penalty for me is very soft, the red card for Ollie Watkins is very, very soft.
“The word I would use is confused because I don’t know where we are any more with decisions like that.
“We saw an incident with Raheem Sterling (for Manchester City) on Saturday when a penalty wasn’t given, that is with our so-called technology checking it.
“Today’s was. We are all left scratching our heads. Maybe I need to coach my players like Keinan Davis, when he goes through at the end, to stick the brakes on, wait for a touch and go down to earn a penalty?
“I am fed up talking about penalty decisions against Manchester United. We have had three dubious ones given against us in the last three games against them.”
Villa were beaten 2-1 at Old Trafford on New Year’s Day when Luiz also conceded a penalty for a foul on Pogba.
Smith continued: “Douglas Luiz should not have planted a foot or given him the opportunity to go down. But is that enough to knock someone off balance?
“We all know it is not. That is why it is soft. On the sending-off, Ollie never appealed (for a foul). He has touched the ball and goalkeeper has come flying out.
“I have watched it five or six times and I can’t tell if there is contact or not. I have asked Ollie and he has said there is slight contact. Enough for him to go down? Probably not. For Ollie to go and get a penalty there, he has to go and get hurt. If that is what we have to do? That is the question over consistency.
“The pathetic rule is we can’t appeal the second yellow. There is no way on this earth the referee can be certain he hasn’t been touched.”