I hate to use a cliche'd question, but it's the most fitting.
I do not know of any ISTJs in the wild, I can't type them, I haven't had any behavior patterns to follow. I do have two ISTJ traits that scream on the surface online.
Very serious in work AND play (big emphasis on that last one)
Very adamant about staying serious
More importantly when I go to prod the suspects in question, they tell me how laid back they are.
Anyone care to bite?