Lots of people count "helping a partner come by using words" (typically by one or both partners masturbating at the same time) as sex; it actually seems to be the default position among sex bloggers. That sounds solid to me; if Alice is doing something to pleasure Bob, it doesn't particularly matter how indirectly. Fewer people (in the list above, Cliff Pervocracy and Greta Christina) count as sex the dirty talk alone, without the possibility of orgasm. I can't think of a situation where that would feel like sex to me, but it appears to work for them. Naive attempts to dissolve the question of "what is sex?" tend to fail because of the assumption that describing the acts is enough, when the psychology is a large part of what the question is getting at. For example, I think that two people masturbating to each other's sight is more like two people masturbating each other than it is like a circle jerk.