The line comes from Rounders, the 1998 poker drama starring Matt Damon as Mike McDermott and John Malkovich as Russian mobster and underground poker host Teddy KGB. In their heads up confrontations, KGB sizes up Mike's nerve and resilience, using a piece of old poker slang. The film became a cult favourite during the 2000s poker boom, and its most quotable KGB lines kept circulating in forums, highlight edits and meme soundboards. This one survived because it works outside poker too, as shorthand for quiet toughness.