An A walks into a bar, orders a beer, and sits down to watch the game. The bartender serves him gladly. A C walks in, sits next to the A, and orders a shot of rye, and a glass of water. The bartender looks ponderingly at him, but serves him up. An E walks in, sits next to the C, and before he can get his order out, the bartender throws all three, the A, the C, and the E out of the bar, with great vim and vigor, and tells them not to come back. Why ?