Khloe Kardashian's Nipples Debut on 'X Factor'

Khloe Kardashian's boobs stole the show on "X Factor" last night ... this according to Simon Cowell who said he was so distracted by KK's tatas ... he could barely focus.

During Khloe's debut episode as a co-host -- along with Mario Lopez -- it became very apparent that KK wasn't wearing a bra underneath her extremely sheer top.

At one point, Simon pointed out that Khloe was pointing out ... saying, "May I say Khloe, you're looking very sexy tonight ... I think the air conditioning is on high."

Khloe shot back, "You love it" ... Simon, "It's very distracting."