The main reason I consider myself demisexual is that the actual 'sex' part of sex doesn't interest me. It's the things that I get during sex other than physical stimulation that make sex valuable to me. Things that make sex worth it for me are...
1) energy play that is easier and more intense because my body is revved up (exercise or roughhousing play works for this too, or some drugs I'm sure).
2) the intimacy of having someone watch my body and listen to my sounds when I am totally uninhibited. (being very drunk and dancing would provide this too, but is more work and expense).
3) the emotional high that my allosexual partners get from sex which makes them more relaxed and affectionate, sometimes for days after.
4) learning about someone in a wordless way through their reactions and desires.
5) in-depth discussions of feelings. I don't get much out of sex despite the above unless we talk out the experience afterward. This has been a difficulty for me because frankly most people are really bad at talking about sex and not great at talking about their feelings either, but I've had the occasional lover who was naturally good at it and others deliberately built their skills.
I don't experience any particular touch as always sexual, not giving or receiving. Nor do I experience any touch as inherently non-sexual. For me, sex is about intention more than anything else. I can't stand for my non-sexually-meant touch to be taken as sexual by someone else. Even if I am in a sexual relationship with them and often enjoy sex with them, if I am not wanting and intending sex, I don't want my touch to be taken that way. Along the same lines, I can often miss "I wanna have sex" signals because I don't apply sexual thought to touch unless that is invited. Someone once literally put their face in between my breasts and I did not interpret this as an expression of sexual interest (later they told me that it was and I realized that most people would probably have taken it that way).
I sometimes enjoy giving/receiving touch that would usually be sexual as purely sensual instead. Touch with that level of intimacy minus the urgency of sex makes for the most tender touch I can imagine. But then, I am not sure this translates for other people because my body still responds in a sexual way eventually. It just feels completely different and makes me almost want to cry (not in a sad way, but like I'd cry at a particularly beautiful piece of music). I've experienced this with Topaz, Kylei, and (to a much lesser extent) my ex-spouse.
I do like the physical sensation of touching other people's genitals. If not for all the mental associations, I would probably like to touch them often in non-sexual ways. That is, not for sexual pleasure but because they feel nice, warm and soft and close. I could cup my hand around them and have it held in place by their thighs which would feel very intimate (whether they were clothed or not). If not for people being ticklish or otherwise uncomfortable with the idea, I'd probably enjoy putting my hands in people's armpits for the same reason.
I like kissing for prolonged periods of time in certain positions and at certain moments. If my nostrils are both clear and we are sitting/laying/standing in a way where there is no weight on my chest and my nose isn't getting squished, so I feel like I can breathe, I like it. But I hate that feeling of being smothered and I will pull away quickly when that happens. I am also sensitive to if someone else is getting squished (that is, if I feel like I might be making them feel smothered, I can't enjoy kissing them even if I can breathe easily, probably leftover habit from being with someone with asthma). I don't like mouth-kissing randomly or briefly because for me to enjoy it I have to be fully into the moment, which takes effort, so I either want to be kissing OR cuddling not usually a mixture. My cuddly-kisses are usually on everyplace other than the lips.
I've never had the chance to kiss an asexual or demisexual person (as far as I know). I feel like I would experience that kissing very differently. I have found that I experience kisses much more sexually with someone who thinks of kissing as inherently sexual, so I imagine that with someone who didn't experience them that way I would get to feel what kisses are like without any sex in them. I am not entirely sure that I would not have a bodily response that would seem sexual (I often shiver and twitch) so I would want to try it with someone who wouldn't find that troublesome.
I don't know if I could enjoy non-romantic kisses on the mouth. I've tried it once and it didn't appeal; I think mouth-kissing is the most romantic kind of touch, for me, except maybe kissing someone's sternum. Of course, romance and sex are completely separate entities for me, which is a whole other post.