Gen Con is a convention that is essentially a massive collection of miniature wargaming, boardgames, D&D related awsomeness, and other things to go along with it. It is in this anons humble opinion that anyone claiming to be a neckbeard should go at LEAST once (or have already done so). Not directly /tg/ related but very, very, cool. Your mind will be blown.
Gen Con is held in Indianapolis, Indiana yearly. The convention is a 4 day affair, running in mid August (often coinciding with the Indiana State Fair, YOU HAVE BEEN WARNED). Bring a backpack for swag (the good kind) and your own water (otherwise $6 a bottle).
Gen Con works a bit differently than most conventions, as most of its events revolve around specific times and games that require a list of players. As with most, you purchase a badge to actually get access to the con (usually around $90), then spend the next few months browsing their fuck-off huge catalog of events - mostly board games, Magic tournaments, and actual pen and paper games. You can either sign up on the website for your choice event, which nets you a guaranteed seat at the table (provided you show up on time), or purchase generic tickets for about $4 a pop that work for almost every event, but are provisional - you only get in if there's room. If there's 10 seats and all 10 are filled, tough shit.
Most of the weekend is usually spent taking pictures, wasting money in the giant dealer room and playing games you've never heard about. And getting drunk.
Gen Con 2016
Where: Indianapolis Convention Center, Indianapolis, IN
When: August 4-7, 2016