The Manning bros hosted their final broadcast of "MNF" for the Rams vs. Cardinals Wild Card matchup on Monday ... and just like Travis Kelce and Marshawn Lynch before him, Peyton said a dirty word.

The moment happened late in the first quarter, when Eli asked Peyton to break down a touchdown play ... but some technical issues led to a much better response.

"I can't hear s***," Peyton said in frustration.

Eli -- who also had his own mishap by flipping his middle fingers earlier this season -- was quick to distract fans from the expletive ... saying, "NEVERMIND!!"

Peyton later explained what happened ... saying his mic busted when he got too excited after Odell Beckham's touchdown catch, causing the technical difficulties.

Peyton then switched the focus back to the game ... going about his analysis like nothing happened, but viewers were quick to share the funny slip-up on social media.

It's now the third time someone on the live "Manning Cast" said a bad word -- as we previously reported, Marshawn was unfiltered during his appearance back in October, with Peyton apologizing on his behalf.

"I want to apologize for some of the language. It's not what we're trying to do on this show," the 2-time Super Bowl champ said at the time.

Before that, Kelce accidentally let an S-bomb of his own slip while chatting with Peyton and Eli back in September.