Intimate relations between members of Model United Nations (known as "MUNdoes," (em-U-en-does)), of which there are three degrees:

Third Degree MUNcest: occurring between MUNdoes of different committees at a conference
Second Degree MUNcest: occurring between MUNdoes of the same committee at a conference
First Degree MUNcest: occurring between MUNdoes of the same school/program.

While first and second degree MUNcest are in fact smiled upon in many circles, 1st Degree MUNcest is widely frowned upon. Those guilty of 1st degree are to be subjected to friendly teasing such that the crime may never be forgotten.

There is also a legendary and unproven MUNcest with ones chairpersons. Many dismiss this to be mere folklore but experts claim it is theoretically possible. It however has not been worked into the degree system and is largely shrouded in mystery and conjecture.

When you eat dirt for the first time and leave your family to build a shack in the woods

Amendment to above definition by Kris-Nigel:

"While first and second degree MUNcest are in fact smiled upon in many circles,"

should be read as:

"While SECOND and THIRD degree..."

the act of dating/hooking up with another student in the Model United Nations program