sneaky tits 

The breasts of a woman that appear at first to be in the A-B cup size range while in a chick's shirt or sports bra, but once exposed and discovered by a fine gentleman, are truly a set of C-D cup titties that run shit and gain a lot of appreciation.

or the inverse;

The meat balloons of a woman that she has artificially enhanced through the use of padded bras or other devices that result in false advertisement for dudes a.k.a. Displaying a healthy set of C-D titties but really having A-B titties we don't really give a shit about and can't tit fuck.

Vince: Yo Will, how'd shit go with that broad you took home from Nikki Beach last night? Looked like she had a sick body but an average set of titties.

Will: Bro i meant to call you this morning....I took that chick home, started going at it with her, and when i took her shirt off, a set of sneaky tits popped out. I couldn't believe it. I was expecting a small perky rack and then a set of D puppies hugged my face. Good time bro.

or

Vince: You aren't gonna believe this bro. Remember that broad I brought home that had those tits we were high fiving about?

Will: Yeah of course son.

Vince: Yeah they were fucking sneaky tits. I feel ripped off.

Will: No way!!!! Victoria from Victoria's Secret is a cunt for inventing those bras.

sneaky tits by Jesus the Prairie Dogg August 27, 2011

Sneaky big tits 

Girls who don't appear to have large breasts in their daily wardrobe but then when seen dressed to go out do, in fact, have bodacious ta tas.

Usually she wears hoodies but if you'd seen her at the club you'd know she's a sneaky big tits.

Sneaky big tits by Jonny Jonzes March 18, 2017