The text plays on the double meaning of the phrase 'beats'. In the context of card games, a 'royal flush' is the highest hand in poker, but the phrase suggests that a .45 (referring to a .45 caliber handgun) 'beats' or is more powerful than a royal flush in a non-gaming, literal sense. This creates a humorous juxtaposition between the rules of poker and a real-life scenario.
A . 45 beats a royal flush EVERY TIME