When the collar of a Jacket has been pulled down, usually to expose the Breasts.
Not to be confused with Jacket Lift (lifting up the bottom of a jacket to expose the chest) or Jacket Tug (tugging down the bottom of a jacket to cover the crotch).
Also, not to be confused with Collar Tug which is for when a character pulls out on the collar of their shirt merely to let fresh air in or to show nervousness, although if it results in the exposure of the breasts or cleavage, it should be tagged as both.