First of all, please don't get offended from the title, and if you don't know what this is look at this video (Warning: NSFW).
I have seen online communities over the years, and the amount of foul language is really high. People are not polite to each other and flame wars are common.
Why is this community is so well-behaved? I don't see the moderators cleaning up the site, which means this is just the users being well-behaved. Do you have any idea why this is only happening on Stack Exchange?