The nip slip might just be the trickiest wardrobe malfunction to spot. It's swift, it's subtle and there are so many shades of gray involved.

This brings us to our latest head-scratcher: Mariah Carey's onstage look at the So So Def 20th anniversary concert last Saturday. Did the singer actually have a wardrobe malfunction or is she the victim of unfortunate shadowing?

The 42-year-old was all smiles as she performed alongside Jermaine Dupri, but nobody seemed to alert her to the fact that her low-cut dress was dropping into dangerous territory. The white bustier number wasn't exactly the most, er, supportive look.

Since we're having such a hard time pinning this one down, we'll file it in our brains under the same category as Jennifer Lopez's dress from the 2012 Oscars and try to forget the whole thing.