It's the very first rule of talking smack: If you're going to say something, you have to be able to back it up. Unfortunately for these athletes, competitors and online arguers, they clearly didn't know who they were messing with.

There's nothing more satisfying than putting somebody in their place to shut them up, and that's exactly what happened in these 21 examples of failed trash talking.

Before overtime in 2004’s NFC championship game between the Seattle Seahawks and Green Bay Packers, Seahawks quarterback Matt Hasselbeck proclaimed, “We want the ball, and we’re gonna score!” He proceeded to throw an interception, giving Green Bay the win.

Pre-karate match intimidation goes wrong.

Conor McGregor tells Nurmagomedov he’s an “amateur,” before getting knocked out.

Paul Pierce and Glen Davis “guaranteed” a Boston Celtic title in 2010. Instead, they lost to the Lakers.

French swimmer Alain Bernard was quoted as saying, “The Americans? We will crush them. It’s what we came here for,” before the 2008 Beijing 4x100-meter relay. He blew a half body-length lead on the final leg to give America, and Michael Phelps, another gold.

Jadeveon Clowney trash talks Leshaun Sims only to watch him haul in a game-sealing interception.

Dude threatening people with a knife gets taken down from behind by police in Brazil.

Tennis player owns a heckling fan.

Dude kisses opponent on the lips and gets knocked out before the fight officially begins.

Dude littering and bad-mouthing gets told off.

Dota 2 trash talk fail.

Knicks superfan Spike Lee talked trash to Reggie Miller, who went on to have an iconic game.