Lewd, rude & crude qualities are universal bonding behaviour, and correct use is really quite difficult. They signify an independence from an imaginary neutral citizen. This imaginary citizen is to some extent who we think we should be; a politically correct, caring, trusting type of person. However it resembles a mannequin in terms of personality, and when we want to connect, we want to connect personally. So we upset the culture of politically correct neutrality which pervades public spaces, and reveal some hidden wickedness which, more often than not, indicates our private desires & / disgusts.
This three things can be fairly consistently categorised into three, lewd – sex, rude – everything not in the other two categories, and crude – stupidity. These three things are common areas of shame and so we have a natural instinct to keep them hidden. They are detrimental if held forth in most of our lives, catching a bus and behaving in one of the above ways is likely to get one filmed, uploaded to the internet, and the final coup de grace is mockery on national television. It may be important that these behaviours, although bad, are not criminal and are better understood as cultural mores.
Although there are further taboos beyond the three eponymous here, they are further developed and do not come as naturally to the psyche. It is not uncommon in my life to be asked questions about wage, although questions of savings and superannuations are rare. Briefly on that last subject, I worked, earnt some few thousands in an account and changed to casual work. It all dried up, somehow every morning my money was changed as though it could out earn the 0.016 percent of a dollar of interest and this labour of reassigning my relatively minuscule money was the justification of the fees which emptied my account. It enraged me and hurt my attitudes towards permanent or institutionally respectable work. Regardless to carry on with the line of thought being made before that brief sojourn, It is a developed taboo and less natural. Fart jokes, being crude, dirty jokes, being lewd, and slapstick comedy are much more universal as a source of laughter & bonding.