I wanna know what this guys PROBLEM is..?

Okay. so this guy i sit next to in cl with im not sure what his problem is. In cl, he acts completely nice to me and im not sure if he is flirting or being overtly friendly but prob is that but not sure. but when i emailed him online or talked to him on facebook he is extremely mean to me. he also grabbed my "smartpen" without asking me first if he could look at it. uhh...im not even sure now..this is like really bugging me...what are your opinions?!