How mad did the enemies of Jesus get at him? The gospel accounts were certainly not designed to focus on such a secondary issue. Obviously they became mad enough to kill him! People have always tried to get rid of things that are in their way; one of my professors used to say that sin is attempted murder of God.
It will take a bit of background work to get closer to that anger answer. If you are prepared to come along, I can already assure you that we will arrive at a complete answer only on that Final Day.
Some of the writers of scripture liked to highlight certain actions of those in the text by putting them into the present tense. 'Jesus goes here...', etc. In this account Matthew usually does that with verbs of speaking.
One of the first times he does this (after the first few chapters) is in Matthew 9:14. "Then the disciples of John come to him, saying, 'Why do we and the Pharisees fast, and your disciples do not fast?" And Jesus answers their question.
Notice how similar that verse is to Matthew 15:1: "Then Pharisees and scribes come to Jesus from Jerusalem, saying, 'Why do your disciples transgress the tradition of the elders? For they do not wash their hands when they eat bread.'" What is different is what follows: 'And he answered and said to them, "And why do you yourselves transgress the commandment of God for the sake of your tradition?"' Then Jesus goes on to confront them with their evil.
This time Jesus avoids answering their question and gives them a question instead. And this is the time where it mentions that the disciples come up to Jesus afterwards and say that the Pharisees were offended. And Jesus does not seem bothered at all by that.
I would think that they were getting quite mad at Jesus already in chapter 15. And at the beginning of chapter 21, Jesus is cleansing the temple. There he says to the people there, 'You ARE MAKING my house a robber's den." (This use of the present tense, as opposed to the other tenses in the other similar accounts, heightens the evil a bit since they are in the MIDST of doing something wrong at this point in time.) And this account details that Jesus healed the blind and lame in that temple, and he also let the children cry out 'Hosanna to the Son of David' in the temple. The text says that the chief priests and the scribes were mad, and they ask him a question. Jesus answers, but he also asks them a question in response. So Jesus is already having some difficulties with his enemies and their questions.
And, then, the text for this Sunday, starting at verse 23 (of Matthew 21), has the chief priests and elders of the people coming up to Jesus while he is teaching. First of all, it should be noted that interrupting someone is quite rude. These interruptions do not happen often in this account.
They have had it with Jesus. And when Jesus says that he will only answer their question if they answer his, that makes it even worse. And, due to the difficulty of the question, when the enemies of Jesus do not answer his question, they are stuck.
At the end of the text for this Sunday is an option that a few more verses can be read (v. 28-32). What makes it worse is that then Jesus gives them a super-easy question to answer. Remember that Jesus is asking this question of the 'spiritual elite'. So I can see this question putting them over the top.
Jesus asked his enemies a question, a choice between two sons, which one did the will of the father. At this point I can see them mad enough at him where they refuse to say the right answer. And that is indeed an option with some of the manuscripts. But, as I said above, things will be clearer on the other side of the grave. For now, our Bibles have them giving the right answer. And Jesus still lets them have it afterwards.
It should also be noted that this pair of people, the scribes and elders, is the group that gets things done in the end. After Jesus' last sermon, they get together and form a plan to kill him. This is the group that sends out a 'great multitude' to arrest Jesus. This is the group that condemns him. And this is the same group that helps make up the story that the disciples came and stole Jesus' body after his resurrection.
That these people were the elders 'OF THE PEOPLE' makes it even worse. Thankfully, Jesus' comforting words at the conclusion of this gospel account were meant for ALL people.