One of the game shops I play EDH at has a rule that infinite combos are allowed, but if you combo out within the first 15 minutes of a game, you forfeit one of your prize packs.

To me that seems like the best way to discourage unsportsmanlike behavior without actively singling out players or styles of play. You're the shop, so you can't discriminate on who's allowed to play at your store, but you can set the rules up in a way that discourages your patrons from interacting negatively with each other. Most antisocial spikes (players that want to win without caring about people's feelings) only care about the rewards of winning, which is usually prize packs or money. If you set the rules up to give them less rewards for being unsporting, they typically cave.

Whatever you do, make your rules clearly defined. Players don't like it if rules are vague because they feel like you can arbitrarily enforce them. You can't simply ban infinite combos or non social play styles because there are so many of those, and it's very subjective was constitutes them. A minimum time for EDH games, on the other hand, is very clear cut.