Ariadna's nipple slip actually happened in front of all the other remaining female houseguests, and Brandi of all people was quick to point it out and comment that Ari has "cute nipples" - we agree. Ariadna had been walking around in a robe and was putting a top on when the slip happened - the look on her face after showed us that she knew we had all just seen her boob.
The amount of nudity in the Celebrity Big Brother continues to surprise us since A. these are celebrities that know everyone wants to see them naked and B. this season is only 3 weeks, which is usually how long it takes for the regular houseguests to stop being careful about the cameras.