Going to be starting something new. It is, perhaps, a little mean-spirited, but very cathartic. I am going to start chronicling the... let's say "less than perfectly socialized" people you tend to meet at cons. Since I mostly go to anime cons with the occasional cross-geekery or sci-fi con thrown in, the list will be skewed in those directions. For our first entry, let's all meet...
Identifying Features: Conversation Guy is always a white male in his 20s or older, usually bearded and overweight, and always poorly groomed. There is no particular reason why these features should be so, but I have encountered many different Conversation Guys, and the patterns are consistent.
Habitat: Any panel, but especially ones to do with a technological or science-fictional topic.
Notable Behaviors: Conversation Guy's primary characteristics are a total lack of consideration and an inability to distinguish between a panel and a personal conversation. Conversation Guy will thus respond to every single thing the panelists say as if the rest of the audience were not in the room and instead he and the panelists were hanging out together, shooting the breeze.
Effective Countertactics: Snark. Conversation Guy is typically desperate to prove his knowledge of the panel topic, so puncturing his fragile little ego is a great way to shut him down. If you are in the audience, and Conversation Guy is disrupting the panel, ask him why his name isn't in the program, since clearly he thinks he's on the panel. If you are a panelist, try pointing out that you don't go to his panels and talk over him.
Cautions: Do not set your Conversation Guy sensors too high! Bearded, poorly groomed, overweight white dudes and people with poor social skills are both fairly common at cons, and so is the intersection. Don't immediately jump down the throat of anyone who, in a moment of passion, responds to or corrects a panelist, especially if the panelists seem okay with it! On the other hand, if an audience member seems to be talking more than any of the panelists, you have a case of Conversation Guy on your hands. Shoot to kill; you are doing everyone a favor.