The go to move of bad poker players. A river rat is a player who, despite holding bad cards and hitting nothing on the flop, continues to bet right up until the fifth and final community card, the river card. More often than not noobs such as this usually get lucky on the river and insist on bragging about it despite the fact that their success was down do dumb luck and not skill. A river rat doesn't know when to fold and due to their ignorance pridefully consider themselves aggressive players rather than crap players, which is what they are. The most agonizingly annoying thing about river rats is that they have a tendency to be arrogant when they suck out, completely oblivious to the fact that they wouldn't last 2 seconds in a real tournament.
Guy 1 - Man check out that douche, he went right to the river with a stinking deuce seven off suit and sucked out running sevens.
Guy 2 - I know aye, and look at that smug smile on his face, acting like he's an expert poker player when really he's just a noob river rat tosser.