titsion
The stretch marks, on a shirt, between the breasts. Especially noticeable when the shirt is tight, the breasts are large, or both.
Look at her titsion. Her tits must be huge to make that much titsion. I'd like to release the tension in my pants between her titsion.
Surface titsion
When you wear a bra too small and your books almost spill out, but not quite.
Did you see the chick in the orange shirt? She has perfected the art of surface titsion.