Intelligent sociopaths generally don't go around telling people that they're sociopaths (or words to that effect), because that would put others on their guard and make them harder to get things out of.

The usually won't say it in a way that the would predict will put other people on guard. On the other hand that doesn't mean that they don't say it at all.

I don't find the link at the moment but a while ago someone posted on LW that he shouldn't have trusted another person from a LW meetup who openly said those things and then acted like that.

Categorising Internet Tough Guys is hard. Base rates for psychopathy aren't that low but you are right that not everyone who says those things is a psychopath. Even that it's a signal for not giving full trust to that person.