Mona Lisa cleavage
Showing a minuscule amount of cleavage; anything less than an inch.
Jane promised to show us her boobs, but all we got was some Mona Lisa cleavage.
Mona Lisa cleavage
When a cleavage looks kind of perky and happy but also a little on the sad any unperky side at the same time.
"Have you seen Emily's breasts? Her tits are like "Wow!" but also kind of "Meh." at the same time... I feel like her cleavage is somehow smiling at me--but also frowning at me! It's like she's got that whole Mona Lisa Cleavage thing going on. You know, like auntie Sara."