I'm always convinced that I'm right.
Because I am a history grad student, I nitpick any movie within two hundred years of my chosen time period (high to late middle ages, although early middles ages and the classical period get this treatment as well). "Well, really, when that knight was fighting off the dragon, his armor was clearly from the early modern period, not medieval. What do you mean, if I can deal with a dragon, I can deal with his armor?"
I have a tendency to simply stop speaking in the middle of my sentences, convinced that the other person can somehow intuit what I wanted to say. "Well, sometimes I think mac and cheese would just be...." *trails off and gazes thoughtfully at the wall*
I also have a tendency to end sentences with "You know what I mean?" when it is not in the least apparent what I mean. "It's just like... when purple and triangles have an illegitimate child and then school it at Hogwarts but then it turns into my cat. You know what I mean?"