Peter lists a series of vices that were acceptable in the Greco-Roman world. Some of these are associated with entertainment (theater, the games), others may be associated with banquets in the temples. While some of these might be family celebrations and fairly innocent, a meal at a temple would be an opportunity for drunkenness, gluttony, sexual excess.
Sensuality (ἀσέλγεια) refers to a “lack of self-constraint” that goes beyond what is socially acceptable. Traditionally this is translated as “licentiousness” and turns up in sin lists along with fornication. It is the kind of insolence that makes a mockery of what is considered acceptable in polite society.
Passions (ἐπιθυμία) is the typical word used for lust, although that is not always a sexual lust; gluttony, for example, is an inordinate craving for food, etc.) The word can refer to any sort of desire that goes beyond what is necessary.
Drunkenness (οἰνοφλυγία) is not the typical word used in the New Testament for one who gets drunk, but implies that the person is gluttonous for wine. Philo of Alexandria uses this word in his discussion of coveting:
Philo, Spec. Laws, 4.91 When it [coveting] affects the parts about the belly it makes men gluttonous, insatiable, intemperate, debauched, admirers of a profligate life, delighting in drunkenness, and epicurism, slaves to strong wine, and fish, and meat, pursuers of feasts and tables, wallowing like greedy dogs; owing to all which things their lives are rendered miserable and accursed, and they are reduced to an existence more grievous than any death.
The word translated orgies (κωμος) refers to a festive meal usually in honor of Dionysus/Bacchus, the god of wine. The word appears twice in the LXX, in 2 Macc 6:4 it describes the revelries of the Gentiles in the Temple courts before the Maccabean revolt, and in Wisdom of Solomon 14:23 it appears in a detailed sin list (translated as “frenzied revels.”
2 Maccabees 6:4 (NRSV) For the temple was filled with debauchery and reveling by the Gentiles, who dallied with prostitutes and had intercourse with women within the sacred precincts, and besides brought in things for sacrifice that were unfit.
Wisdom of Solomon 14:23 (NRSV) For whether they kill children in their initiations, or celebrate secret mysteries, or hold frenzied revels with strange customs
Similarly, “drinking parties” (πότος) refers to carousing, although this is not always with the connotation of drinking in a sleazy bar. The elite often held banquets to discuss literature or philosophy (a symposium) while drinking heavily. BDAG suggests that Peter “has less sophisticated participants in mind.”
Lawless idolatry (ἀθέμιτος εἰδωλολατρία). This final item is scathing in its condemnation of the religious practices of the Roman world. The word Peter uses here is used for wanton, unseemly behavior, things that even the Roman world would consider too disgusting. In addition, Peter calls these gods idols, something that would not be considered politically correct in the Roman world. You might not worship someone else’s god, but you did not call it a disgusting idol! Not only do these people commit acts that are unseemly, they do so in the service of a worthless idol.
Peter implies that his readers have participated in some of these things. This is usually taken as a “proof” that the congregation is made up of Gentile converts, since Jews would not have participated in these kinds of debaucheries. But as Karen Jobes points out, this may be an overly idealized view of diaspora Jews living in a pagan culture. That some of them at some point did attend the theater or the gladiatorial games is entirely possible.
Christians developed the reputation for being different because they chose not to participate in such behaviors. In the ancient world, different was always bad. If a Christian choose to not participate in some civic event because it is an excuse for debauchery, they are likely going to be view with suspicion. If the event was dedicated to the gods of the city, perhaps the Christians were endangering the prosperity of the city. If the event was a family celebration, then refusing to participate would have created tension within the most basic unit of Roman culture.
This goes beyond modern Christians abstaining from the drunken festivals of our time. To use the analogy of Mardi Gras, if someone refused to participate in the festivities, they might be considered a kill-joy, or holier-than-thou, or judgmental. But few would consider them traitors to the city of New Orleans, and no one really thinks that the gods are going to bless the city since everyone participates in the revels. This radical call to holiness opened many early Christians to accusations of disloyalty.