Obviously ESTP.
ESTP's auxiliary function is Introverted Thinking. They have a strong need to think, especially if bored with their current situation. Like at work, or if forced to sit still, or too tired to move, they will probably obsess over something, at least that's what I do. It's like having a monster inside your brain constantly grinding its teeth and whispering -use me. Use me!- But, they could be secret nerds, because they are not researching stuff to brag or to share their knowledge and they don't care about becoming experts in the field, they are only doing it to let out energy and not go crazy. If I couldn't nerd out on the Internet when bored (which is often) I'd be out all the time, wandering about town, spending all of my money, getting drunk, blowing up people's phones, smoking a ton of cigarettes and magnetizing trouble. I have a lot of knowledge I have gained by accident, just because I need something to google about. Then when I feel like I've figured it out or I just don't get that feeling of newness and shine anymore I move on, have a phase when I don't think or read abot anything for a while, until I find something new.