False teachers will often accuse you of being a false teacher if you disagree with them.
So how can we identify false teachers?
If you read 2 Peter 2 carefully, you will see that what Peter was referring to is more like what many of us would call cult leaders today. Obedience to Jesus is not an essential part of a false teachers doctrine.
They will have some or all of the following characteristics: they will practice sexual immorality, and be slaves to sin; they are greedy and arrogant; they are liars who twist scripture to make it conform to their own ideas.
But what if someone is honestly mistaken about something the Bible teaches, and they are telling others what they think it says, are they a false teacher? It is true that they would be spreading a false teaching, but that doesn't necessarily make them a false teacher. (The following article by George Sarris is a great little introduction to this subject. Am I Really a False Teacher? )
False teachers label anyone who challenges their teaching as a false teacher or a sinning brother and do not deal with those who challenge their authority the way Jesus said a “sinning brother” should be dealt with. Many will say they are led by the Spirit, or even claim to be the “Lord’s anointed.” They act as though they have as much authority as one of the original apostles. Because of their “position” they say they have more authority than ordinary Christians.
False teachers do not submit to Jesus authority when it comes to dealing with “problem people” in their church. (This is the stick they use to expel the “sinning brother" without going through the process Jesus commanded. Some churches have adopted false teachings and some of those churches have included the false doctrine in their statement of faith; then they use that proclamation to stifle all future discussion and debate. Like the pharisees of old, they cannot believe that they may have misunderstood the scriptures on some important point. None of us are infallible. We should love truth more than our doctrines. We must be willing to re-examine the scriptures as often as someone challenges something we believe with the claim that, "the Bible teaches." There are no excuses for ignoring the outline Jesus gave for dealing with problem people in the Church. According to Jesus, there are no exceptions to the rule. If the people in each individual church followed what Jesus outlined when dealing with people who taught "doctrinal errors," errors would be identified and doctrines would be improved. If throughout church history “heretics” were dealt with according to the pattern Jesus outlined, the church would be much better shape today.)
Now let us suppose you believe someone in your church is a false teacher. Should you talk to the pastor about them? Should you talk to that person in private? Should you wipe the dust off your feet and refuse to talk to them? (Jesus was referring to those who refused to welcome the disciples. So no you should not treat them that way.) Follow Jesus advice when dealing with a trouble maker (whether real or imagined).
Suppose you find out that someone in your church believes in universal reconciliation. Don't go and talk to others behind their back about them. Talk to that person in private. Find out what they believe and why they believe it. Examine the character of this person. Are they an honest person? Are they obeying Jesus? And be careful to obey Jesus yourself by following the commands Jesus gave when dealing with someone you have a problem with. If you are unable to come to a consensus with this person about what the Bible actually teaches, take it to the next level (see Dealing with a sinning brother). But don't be in a hurry to do so. For as we judge, we will be judged. Prayerfully examine the arguments in light of scripture.
Now having said that, the man in the following video may fit the category of a false teacher. I can't see how he can honestly come to some of his conclusions. He has some nutty views and I don't agree with many of the things he says. His message in the following video is abrasive. It's so abrasive that I wasn't going to share it on this site. But I decided to because on this particular issue he makes some very important points that Christians ought to carefully consider. He certainly sums up what many people think (see the comments on YouTube).
What he says about this doctrine causing more people to reject God than all the wars and all the oppressive regimes combined may have some truth to it. Japan might have become a predominantly Christian country if it was not for that doctrine (see the video below). Not only has the doctrine caused many to doubt God's goodness, it has been the primary justification for persecution of heretics and Christians by other "Christians." See "A Legacy of Fear and Persecution" in Thomas Talbott's book The Inescapable Love of God.
Nowhere in the Bible does it say that a person has to accept a particular view about the nature, purpose and duration of hell to enter into God's Kingdom. So people who teach that Jesus is the only way to God, but also teach eternal torment, or conditional mortality, or universal reconciliation should not be regarded as false teachers.