As a chuunin, Shikanenai usually uses whatever form or courtesy would be least obtrustive. If he lets his guard down he's generally a hair less polite than the situation calls for and tries not to use people's names much. When he does, it's generally a mark of respect: the only times he does so in SSS thus far, he uses the -sensei honorific.
As a genin, however, he's deliberately being a bit bratty, using Ore instead of Boku, for example. He'll use Sessha if he's being sarcastic, particularly if he's refering to himself and Shikamaru collectively. He's probably refered to Kakashi as Kakashi-kohei at least once when he's caught the jounin out and Kakashi knows it.
D for Drakensis
You're only young once, but immaturity is forever.
As a genin, however, he's deliberately being a bit bratty, using Ore instead of Boku, for example. He'll use Sessha if he's being sarcastic, particularly if he's refering to himself and Shikamaru collectively. He's probably refered to Kakashi as Kakashi-kohei at least once when he's caught the jounin out and Kakashi knows it.
D for Drakensis
You're only young once, but immaturity is forever.