Sexual position involving a partner with a penis and a partner with breasts.
The partner with the breasts lies down and has their face sat on while giving a rim job to the other who, facing the direction of the breasts, uses said breasts to stroke their penis.
Similar to 69, a Sitty-9 is when a couple is laying in the position, but fully clothed and not having anyoral sex. A very raunchy and cute thing for couples to do, so long as neither of them farts.