Interesting. Whenever I see aggressive confidence in an interviewee, I immediately think Dunning-Kruger because statistically it's by far the most likely cause. Either way it's down to empirical evidence though.
Anyway, as far as anecdotal evidence goes, I tend to intentionally give off a pretty neutral vibe and rarely worry about flunking an interview. (I chalk it up to mad skillz rather than body language though.)
One could also argue that your willingness to quickly diagnose an individual coping with a traditionally high-anxiety situation (interviewing) with trendy cognitive bias issues calls your ability to recognize your own weaknesses into question.
Anyway, as far as anecdotal evidence goes, I tend to intentionally give off a pretty neutral vibe and rarely worry about flunking an interview. (I chalk it up to mad skillz rather than body language though.)