Snoopy is not just a cute cartoon dog. The Snoopy Deformity (also known as the waterfall deformity) is when you have natural tissue which falls off the breast implant, leaving a full upper pole cleavage area, and a hanging natural breast.. 
When do you have to worry about this?
The most common scenarios for this issue come from when:
- you have a fair amount of natural tissue (meaning C or D+ cup) which is loose and droopy. You get a breast augmentation with an implant, trying to avoid doing a lift. With time, natural tissue ages. Implants don’t. So what you see is the natural tissue “slides” off the implant, resulting in the downward pointing nipple and a weird shape to the breast.
- you have a breast lift of your natural tissue (again C or D+ cup) with placement of an implant. Initially they may be well centered and look good. But again, over time, the natural tissue ages and the implant does not, so the natural tissue slides off the implant. You do not see this as much when you have a small amount of your own tissue (A or B cup) because there is not as much “weight” to your tissue, so gravity does not affect your natural tissue as much.
Do all breasts do this?
No. It really has to do with having a lot of natural, aging tissue mixed with an implant. As you age, your tissue quality changes and loosens, particularly around menopause. Other things which can exacerbate the issue are major weight changes, pregnancies, and breastfeeding- all of these will hurt the elasticity and “bounce back” of your breast skin.
Can I prevent it?
When I do a breast lift, I do a lot of internal sutures to shape the breast. This is to try to keep it from aging. Wearing support is good, as it will help keep your natural tissue from stretching out and aging with time and gravity. Avoid things which hurt the elasticity of your breast skin and tissue, like major weight changes, pregnancies, and breastfeeding after your implant surgery.
When I do the initial placement, I try to position the implant lower in the pocket and the natural tissue high, to keep the breast tissue and implant centered for longer.
The biggest thing you can do is consider DO YOU *NEED* AN IMPLANT when doing a breast lift. I saw a patient today who is happy with the size of her breasts, just not the shape and position. She is a C/D cup. The question is: should she do a lift with an implant or just the lift? The traditional teaching when I was in plastic surgical training is “all women need an implant” when they do a lift to get a good shape and fullness. With the advent of the vertical short scar breast lift, I do a lot of internal suturing, and I feel the shape of my breast lifts is good without an implant. So from my viewpoint, you use an implant only when you want or need the volume, not to help shape. Particularly if you have a C or D cup naturally, if you put in an implant you are opening yourself up to the potential issues of implants (malposition, capsular contracture, leakage, infection), you will likely need an additional surgery at some point (to replace the implant), and you may get the snoopy deformity, which is not pretty.
So keep Snoopy in the Sunday comics.