Lasciviousness means to be provocatively lewd, or to make a show of obscenity. Jesus Christ included lasciviousness among "the evil from within."
"7:21 For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, 7:22 Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness: 7:23 All these evil things come from within, and defile the man." (Mark 7:21-23 KJV)
The actual Greek word of the Holy Scriptures that is translated as "lasciviousness" is pronounced as-elg-ia. It literally means incontinent, but was also used to mean the same as lasciviousness - to make a show of sexual obscenity.
"Let us not be desirous of vain glory"
Converted people who have freed themselves of lasciviousness must always remain on guard against returning to the wrong way (see the Fact Finder question below).
"12:20 For I fear, lest, when I come, I shall not find you such as I would, and that I shall be found unto you such as ye would not: lest there be debates, envyings, wraths, strifes, backbitings, whisperings, swellings, tumults:
The ways of gross carnality (note below how many ways it manifests itself) are the ways of death. The ways of spiritual purity are the way to life.
"5:19 Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, 5:20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, 5:21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.
Paul was "the apostle to the gentiles" - the reason that he directed his teaching to them specifically.
"4:17 This I say therefore, and testify in the Lord, that ye henceforth walk not as other Gentiles walk, in the vanity of their mind, 4:18 Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart: 4:19 Who being past feeling have given themselves over unto lasciviousness, to work all uncleanness with greediness.
Peter was the apostle to the people of Judah, but his teaching against lasciviousness was the same as Paul's teaching to the gentiles - both of which were the same as Christ's teachings to everyone.
"4:3 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: 4:4 Wherein they think it strange that ye run not with them to the same excess of riot, speaking evil of you" (1 Peter 4:3-4 KJV)
Fact Finder: What is "concupiscence"?