To talk over people's heads using technical jargon that they're not going to understand. It's designed to equivocate others and to make them feel intellectually inferior. Especially when one is extremely irritated, aggravated and indignant. It's like the geek version of going ape shit, only in a more verbal, cerebral, subtle and restrained type of manner.
I could tell that Steve was going geekshit on Stan, Samantha and Mike this morning in the office. He was lecturing them with those big and unfamiliar words. They had no idea what he was talking about, making them feel stupid. It was his subtle and oblique way of showing how unhappy he was working with them.