I agree with Foxglove. Cheating entails doing something that one has explicitly or implicitly agreed not to do by entering an exclusive romantic relationship with another. Precisely what one has agreed not to do may depend on the particular situation - there are such things as open relationships, in which in some cases that openness is subject to agreed limitations, but in general, it is sexual and romantic intimacy in respect of which people implicitly undertake to be exclusive to a spouse or other partner.

There is no easy or precise definition of when conduct becomes intimate. As Foxglove points out, something inducing arousal in one person is not by itself sufficient - merely looking at an attractive member of the opposite sex can induce arousal, and that can hardly be described - by itself - as intimate. Even in circumstances where both persons are aroused, this is not necessarily sufficient for intimacy (imagine two very good looking people wearing revealing clothing meeting briefly on the street, for instance).

A reasonable rule of thumb is that an intimate act is one that one would not perform (or permit somebody else to perform upon one) except if one was aroused by it and by the person with/by/to whom it is done. (Things might get rather complicated if this is so for one but not both people who jointly and willingly engage in conduct that is not conventionally considered as intimate; it might be said in that case that the act is an intimate one for one person and not the other; it is doubtful in the circumstances that the other can be said to be cheating on an implicit undertaking not to be intimate with another, especially if he or she does not know that the other treats the act as if it were intimate.)

In the context of our particular proclivity, things are not altogether straightforward, as much of what is involved - eating and giving food to others or encouraging them to eat - is not something that people do tend to reserve for situations of intimacy. We all have to eat to survive, and eating is conventionally a social pastime. Feeding other people - in the broader sense of that term that includes dinner parties - is a common social occurrence amongst people who do not find it remotely sexual (even if the eating involved is of the overindulgent type that many of us enjoy). Those of us who do find it potentially sexual will still wish to engage in the ordinary social events in the ordinary way, and may well find a non-sexual joy in doing so in addition to any sexual arousal that might follow from particular permutations of interaction.

Foxglove might well desire to be "done" by somebody who encourages her to eat a huge cake, but my joy in baking cakes and feeding them to other people comes in large part from the social element and the satisfaction in others enjoying what I have made (that is not to say that an attractive woman eating a goodly amount of it does not have its own special joy, of course). For many, I suspect that the situation is very similar.

Thus, it seems to me that only those activities so risqué that one would not engage in them other than with somebody by whom one is aroused can be those by which one might be said to "cheat" in a conventional relationship, but precisely where such activity begins and ordinary social activity ends is likely to be unclear in many cases.

This'>www.economist.com/news/science-and-technology/21586269-how-bacteria-your-gut-may-be-shaping-your-waistline-wider-understanding article from the Economist might be of some interest here.

Actually, "how do you do?" is not an enquiry about one's health - it is a general greeting. Some may consider it somewhat formal, but there is a great deal to be said for formality and politeness, unfashionable as they are: the formal rules of politeness have been forged over many years as a means of considering others' convenience and feelings without having to second guess what the person actually wants out of an interaction. They are properly loosened when people are familiar and friendly with each other precisely because that familiarity enables people to know more about what will be convenient and acceptable to the other than with a stranger and because being on friendly terms means that the people in question get on with one another enough to desire to be in each other's company by choice.

The modern fashion for being casual and familiar with complete strangers is a serious mistake, and gives licence to strangers to impose upon people who would rather be left alone, and many other such interferences with the commodiousness of people's existence that the rules of politeness and formality were intended to, and when used, do successfully preserve.

There is also the "Food porn" group on Flickr.

A variety - but the average is average sized.

I'm sometimes inclined to respond with, "Sorry: do I know you?".

Saying/writing "how are you?" to a complete stranger is not polite. "How do you do?" is the polite greeting, which does not mean "how are you?".

The reason that "how are you?" is not a proper way of greeting a total stranger is that it is both obviously insincere (why should one care for the health of a total stranger any more than one cares for the health of the world at large, to whom one does not ask the question) and excessively personal: one should not be asking about the personal affairs of total strangers.

If, despite their greeting not being polite at all, one nonetheless feels obliged to start a conversation with these people about some or other trivia, the weather is always the best subject: there is always something to talk about, and it is not at all personal. A conversation might thus go like this:

Idiot: "how r u?"
Intelligent person: "Um, very well, I suppose. I don't think that I know you, do I?"
Idiot: "no"
Intelligent person: "Hm. Well, lovely day, isn't it!"
Idiot: "tell me about yourself"
Intelligent person: "I like sunshine!"
(Idiot gets bored and leaves).