I often see this as a response by men; oh she's laughing. She's fine. She's enjoying it.
This reminds me of a time where I noticed a female at work being harassed by a male patron. She was giggling but it was clear from her body language that she was extremely uncomfortable by his actions. When I reported it, one of the men I HAD to report it to pointed out that she was fine because she was laughing. I gave him a lesson right there and then, explaining to him that's how some people cope with uncomfortable situations. Including myself. He shut up right away.
Oh, and they spoke to the female co-worker and guess what? I was right on the money. Great read - thanks for sharing.