Lasciviousness is the sin of lust, sinful emotions, and lewdness. It is filthy and shameless conduct. Lasciviousness is one of the characteristics by which you can recognize false teachers:
For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ. (Jude 4)
In times past you may have been lascivious. As a believer, you are no longer to continue this behavior:
That he no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God.
For the time past of our life may suffice us to have wrought the will of the Gentiles, when we walked in lasciviousness, lusts, excess of wine, revellings, banquetings, and abominable idolatries... (I Peter 4:2-3)
The Bible teaches that if you continue to be lascivious, you will eventually give yourself over to it without conscience:
Who being past feeling have given themselves over unto lasciviousness, to work uncleanness with greediness. (Ephesians 4:19)