“Big Brother” houseguest Kaitlyn went from zero to stupid real quick when she dropped the n-word Thursday night during the show’s online live feed.

She was talking to 2 other guests — Tyler and Scottie — about making a quick transition … when Kaitlyn, who is white, decided it was the perfect time to quote Drake‘s “0 to 100” … and NOT the clean version. She said, “I did go zero to 100 n**ga, real quick.”

Seems like she realized her idiocy real quick too … because she immediately said “Oops,” and continued mumbling lyrics to the song as if to say … I was just singing a song, I’m not racist!

All 3 of ’em must have remembered at that moment producers JUST finished warning them about this kinda crap … after Angela and Rachel worried their tans would make them look too “ghetto.”

‘BB’ producers say the racist language will not be used in the CBS broadcasts.