A cross between the name "Glenn" and "Menstrual" used to piss off, irritate, or simply make fun of those named Glenn. Irrational and unreasonable behavior ocurrs randomly to those inflicted with glenstration. Variations include glennstrual, for those who are really anal. Only applies to Glens between puberty and glenopause.
After too many drinks, he went through a glenstrual cycle.