It hasn’t seemed like Chris Brown has any boundaries when bringing girls on stage for “Take You Down” … but it turns out there’s one line he won’t cross.

One fan just offered up his wife to CB on a silver platter … and the singer certainly wasn’t expecting that.

Chris shut the fan down, laughing with the audience as he said … “I ain’t gonna do that.” And just to make himself extra clear, he doubled down, saying “hell nah.”

CB was rattled by the request to “d*** your wife down” … passing on the opportunity to get down and dirty with a married woman.

As you know, Chris has made headlines for his risque renditions of “Take You Down,” which have involved him really going at it with female fans.