Sexual thoughts or actions, especially those involving necrophiliism, pink fluffy handcuffs, or any sort of playtime done prior to marriage. EXCEPTION: when Jesus says it's ok or when the hankypanky is used for the betterment of those around you.
Jack's use of the "vortex" caused her to moan so loud that not even doing it in the RV could hide the fact that the hankypanky was about to get good.
Anything which can happen between a couple. There is no set definition as to what it may be, but it can be said that it issomething that someone who is not part of the couple would not want to be around when it is occurring.