Here's another example of where social intuition is important, weddings and funerals, and these could vary greatly by culture and generation. While basic ettiquette can be taught (such as not eating the garnishes even though they're edible), this is not usually the issue for people with ASD as much as the more complex issues that require good social intuition and cannot be easily generalized.
I'll use funeral "ettiquette" as an example, "Should I go to the wake or not go?". This is something that varies not only by culture, but on an individual level. While the world's best "ettiquette" books can give helpful guidelines, they can't determine the dynamics of closeness between you and another person. Some people are more private than others, and it's hard to measure the closeness of a relationship in absolut terms. Some of the general guidelines I'm familiar with: If a close relative or friend dies, go to the viewing and the funeral, an acquaintence, extended relative or someone close to someone I'm close to maybe go to one or the other, if the people seem private than a sympathy card may be fine. One has to watch with cards, I'm Catholic and used to the practice of Mass cards, but one has to remember that aside from Catholic and Orthodox Christians (and maybe a few Anglicans), many people don't pray for the dead can can take a Mass card the wrong way. The other thing is if a person dies under controversial circumstances (a suicide, homicide, accident where there is foul play being investigated, something that made the news, HIV/AIDS, an infant's death, or the untimely passing of a young person, even the death of a person who was estranged from their family...) one has to proceed with extreme caution to avoid an extremely awkward- even ugly situation. More cynical types may even misinterpret an attempt at a kind gesture as morbid curiosity. It is then best to get advice from another person such as a parent and a worldly-wise mutual acquaintance. This is not always easy since sometimes people can get hot-headed and patronizing just because you so much as brought up the subject. Sometimes it's best to just say a silent prayer for those involved and keep one's mouth zipped. Other times you could just show up, give condolences, and if you feel awkward just leave. Sometimes in the case of a public figure or a fallen soldier it is OK for even strangers to show up, but usually something like that would be announced. Even if you make a slight faux-pas most gracious people should give people's good intentions the benefit of the doubt. Some people are more direct; I talked to someone who told me of an old mutual acquaintance of mine ending his own life(I didn't even know until a few years after). She was pretty close to him but lost touch before the incident. She still went to the viewing only to be sternly asked to leave. I have a shy streak so I could only imagine how I would have felt if it was me. Also in many cultures a funeral is a somber event as would be expected, but in others there is a more lively and light hearted vibe.
On a lighter note joyous occasions such as weddings may be a little more forgiving. How to dress is important to know but one could always err. on the side of caution. I know in Italian weddings there are sometimes these "Jordan almonds" used as garnishes in these lace bags. If you have strong enough they are actually pretty good, and they were popular gifts, eating them however seems to be just "not done". I think the proper thing to do is take them home and let them collect dust in the china cabinet for a few years. Upscale restaurants have their own rules both unwritten and sometimes written. Some are easy to figure out some are not so obvious such as not asking the price. At least in this case it is pretty easy to get advice from others and a slight faux-pas usually will get us nothing worse than a turned up nose.
I'm not trying to even give advice here, just demonstrate some of the ways good people can get severely misunderstood due to difficulties in social skills and how logic and basic manners or "etiquette" are not always enough.