Question:I can't really remember if I have ever done this, but I am kind of sure I have. I hope I never said this, but if someone says to a person: "If I am lying, may I go to hell," and then they lie, will they go to hell even if they repent?
I am constantly amazed at how many schemes people imagine trying to tie God's hands and claim that He cannot save them. "But if a wicked man turns from all his sins which he has committed, keeps all My statutes, and does what is lawful and right, he shall surely live; he shall not die. None of the transgressions which he has committed shall be remembered against him; because of the righteousness which he has done, he shall live. "Do I have any pleasure at all that the wicked should die?" says the Lord GOD, "and not that he should turn from his ways and live?"" (Ezekiel 18:21-23).
First, does a person, who commits a crime, sends himself to jail? I hope it is obviously not true. A person is too biased to correctly determine if what they did deserves punishment or how much punishment. We have judges to handle that.
For the same reason a person cannot directly decide to send themselves to hell. They can choose to violate God's commands, such that God is left having to send them to eternal punishment, but they cannot go before the Judge of all the Earth and tell Him he has to send them to Hell. It is not a choice that man has been given.
What is actually happening is that a person who makes such a statement is vainly trying to give their word more validity. The problem is that it doesn't change a single thing. A liar could say that and still be lying. It doesn't given the listener any more confidence that he is hearing the truth. That is why Jesus scolded the Jews for trying to boast their believability, "Again you have heard that it was said to those of old, 'You shall not swear falsely, but shall perform your oaths to the Lord.' But I say to you, do not swear at all: neither by heaven, for it is God's throne; nor by the earth, for it is His footstool; nor by Jerusalem, for it is the city of the great King. Nor shall you swear by your head, because you cannot make one hair white or black. But let your 'Yes' be 'Yes,' and your 'No,' 'No.' For whatever is more than these is from the evil one" (Matthew 5:33-37). There is only one way to make yourself believable -- always say exactly what you mean, never lying about anything.
What you should repent of is trying to get people to believe your lies with false assurances.