Would people just let a man grabbing a woman and spanking her happen?
He didn't say "grabbing", and in context, I'd guess that by "spanking" he meant a single swat to the buttocks.
The story is so far off from my priors of how people behave that I think the possibility that it isn't true should be considered.
It says more that you don't get out much, or aren't very observant when you do. I don't get out much, and never got out much, even during the brief few years when I was both single and of age, and such a story as this one is so utterly mundane and commonplace in its elements as to seem scarcely worthy of comment in the first place.
Most guys that protest such behavior from women make some other form of scene than swatting, of course, and most simply whine to their buddies or suffer in silence rather than make a scene at all. But apart from that, it's an utterly ordinary story, and observable many, many times a night in any "meet market" where the women go to dance and drink, funded by deluded potential suitors.
I agree that "spanking" is ambiguous, and a single hit would be plausible.
It's true that I don't get out much in that sense-- I don't like loud noise (as in really hate it) or drunk people.
Followup to: Do you have High-Functioning Asperger's Syndrome?
LW reader Madbadger uses the metaphor of a GPU and a CPU in a desktop system to think about people with Asperger's Syndrome: general intelligence is like a CPU, being universal but only mediocre at any particular task, whereas the "social coprocessor" brainware in a Neurotypical brain is like a GPU: highly specialized but great at what it does. Neurotypical people are like computers with measly Pentium IV processors, but expensive Radeon HD 4890 GPUs. A High-functioning AS person is an Intel Core i7 Extreme Edition - with on-board graphics!
This analogy also covers the spectrum view of social/empathic abilities, you can think about having a weaker social coprocessor than average if you have some of the tendencies of AS but not others. You can even think of your score on the AQ Test as being like the Tom's Hardware Rating of your Coprocessor. (Lower numbers are better!).
If you lack that powerful social coprocessor, what can you do? Well, you'll have to run your social interactions "in software", i.e. explicitly reason through the complex human social game that most people play without ever really understanding. There are several tricks that a High-functioning AS person can use in this situation: