It is a common practice in today's Vaisnava culture to introduce the four regulative principles as part of the initial introduction to Krsna Consciousness: no meat eating, no intoxication, no illicit sex and no gambling. The introduction of these regulative principles is often done without much explanation, as many consider the "four regs" to be fairly simple, cut-and-dried. In some respects, however, that is not the case. There are many gray areas surrounding these four regulative principles that have led to a host of speculative interpretations as to exactly what they entail.
First and foremost, one should keep in mind that these principles have been introduced by the Sampradaya Acarya, Srila Prabhupada, and the disciplic succession that he represents, as being the topmost position. It is the absolute authority's responsibility to present the ultimate principles. And, it is the responsibility of us conditioned souls who are aspiring to achieve Krsna Consciousness to strive to come up to these standards, knowing full well the benefits and the repercussions of either following or not.
Although these regulative principles are presented as the standard, it is up to the disciple who commits or vows to follow the principles to follow them according to his or her realizations. As a society or a culture, it is practically impossible to determine whether someone is actually following the principles and what their motivations for doing so are. Therefore, it is a personal affair, and should remain so. It's been my experience that there has been far too great a 'witch hunt' mentality surrounding whether or not someone is following or not following the four regulative principles. This has led to paranoia, pretension and deception. One of the greatest ramifications of this is that individuals, and even groups, have attempted to misinterpret or misrepresent the absolute authority's position on these principles so they can break them without encountering guilt or social stigma. It's far better to simply be honest with oneself, and to avoid both making a show of following them, or stating that you're following them when you're not.
It doesn't take long in the community of devotees to see how certain individuals have created their own unique boundaries around these principles, whether it be the sexual aspect, the meat eating, gambling or intoxication. For those who are living in the west, it's particularly hard to determine that what you're eating isn't contaminated by some condemned ingredient originating from animals, seafood or other obnoxious sources. One has to go to pretty extreme lengths to guarantee that what you're taking is pure and strictly adheres to the regulative principles.
When it comes to intoxication, it can also be hard to determine whether or not what you're consuming is intoxicating. Of course, there's the standard understanding that intoxication includes drugs, alcohol, and tobacco. Coffee and tea are to be avoided because they contain caffeine, but caffeine is present in foodstuffs in a wide variety of forms today, especially in western culture. Beyond the most obvious intoxicants, there are many substances that create an intoxicating effect but are still considered acceptable enough for consumption by many devotees. Refined sugars and chocolate are good examples of items that fall in this "gray area". In India, certain dahls are even excluded from the list of acceptable foodstuffs because they are so high in protein as to be considered excessively 'mode of passion' eatables. In the end, one must either interpret for themselves, or follow the example set by a specific authority.
There's been a great deal of debate surrounding the idea of what illicit sex is. As we have heard in the Acarya's sastric version, it means ultimately that you simply don't have sex life except on the rare occasion that a bonafide married couple wants to consummate children. Unfortunately, many followers have re-interpreted this to mean just 'no sex outside of marriage', period. Then there are the various conclusions as to what even constitutes sex.... let alone what constitutes marriage. Sex being the most private activity is also the most difficult of all the regulative principles to determine if someone is following or not.
Like the other regulated activities, gambling is also beyond the bounds of our straightforward understanding. We know that gambling includes dice, cards or the lottery, or going to some casino or gaming hall to place bets on sporting events. But there's also a school of understanding that includes mental speculation in the category of gambling. There's another school that feels that any kind of business activity is gambling. Of course, one's whole material existence is gambling: it's a gamble to have children, to open a business, to buy something, or to travel somewhere. Ultimately, where one draws the line on "gambling" is an individual determination.
One of the main principles expounded by Lord Caitanya Mahaprabhu is that devotees should live in community with other devotees. To a degree, this is intended to help one follow the regulative principles by putting a certain amount of social pressure and stigma on whether one is following or not. Of course, in this day and age, such communities are few and far between. Due to economic constraints and various philosophic and political contentions, such communities do not suit a good percentage of the devotees who find themselves living outside the Vaisnava community. These individuals must adjust the four regulative principles to their own circumstances. I don't believe that strictly following these principles is of the highest priority compared to other aspects of Krsna Consciousness, although they certainly have a relative degree of importance. I find that many devotees put the regulative principles on a pedestal that is higher than other far more important aspects for Krsna Consciousness, for example, studying Srila Prabhupada's books and correctly understanding the philosophy presented by the Sampradaya Acaryas.
The main point here is that one has to make individual decisions about where to set their boundaries surrounding these regulative principles. If one is sincerely following the Krsna conscious example set forth by the Sampradaya Acaryas, then in due course of time if their boundaries are off base or below the standards, they'll gain their own individual realizations and will eventually give up certain activities which they've come to understand are displeasing to Krsna and his representatives.