When two people defecate simultaneously back to back. Can occur anywhere, not defined by location. Definition comes from the scene when Forrest and Bubba are in Vietnam and sleep back to back. This is the position two people must take in order to share the same toilet, or to poop in an open field with no support structure to lean against.
Jory and I really had to poop but there was only one toilet. We took a quick Forrest Dump before plunging the clearly clogged toilet.
To defecate onto a ping pong paddle and then tapping your partner in the face to show a loving commitment to the relationship. After the tap the words, "I love you Jenny!" must be shouted even if your partner's name is not Jenny. Made famous by the popular movie, "Forrest Gump" when the main character becomes famous for being a professional ping pong player during the Cold War.
I was going to propose but I wasn't ready for marriage, so I forrest dumped her.