Half Nelson= A normal bowel movement with limited impact to associated porcelain and surrounding stalls.
Full Nelson= A bowel movement in the like of the Mt St. Helens eruption. Usually impacts the entire restroom facility, including stall walls, porcelain, seat and sometimes the floor.
Affectionately named after a construction worker named Nelson.
Brian: Don't go into stall #2, I just had a Full Nelson. Those protein shakes are killing me.
John: Really I only had a Half Nelson this morning...