mensturating
An unfortunately common misspelling of the more accurate term "menstruating". Quite popular on UrbanDictionary.com
Examples abound, far too many to begin to list here. "Mensturating" typically appears to feature in colorful, often crude, articles written by juveniles more interested in the 'gross factor' of their articles than the accuracy of their spelling.
Menstural Monster
The evil entity that comes to women once a month, resulting in said female becoming the biggest bitch of the best.
Ed: Dude, did you see how she blew me off?
Bill: Yea, she's got the menstural monster.
Bill: Yea, she's got the menstural monster.