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1.
manstruate, manstruation
masculine variation on menstruate,
When a man displays behavior that is reminiscent of mood swings brought on by the female monthy cycle.
Brian has been a bitch all day; he must be manstruating.
by Peter Thomas October 12, 2005
 
2.
When a male is going through a period of increased irritability and moodiness.
Geez, Jermaine, what's up with HB? He's been so pissy lately. He must be manstruating. Give him a manpon.
by Cholo79 April 15, 2008
 
3.
The time of the month when men display the same characteristics of women during their "time of the month." Generally consists of elevated bitchiness, lack of compassion for others, and intense hunger. Steer clear of boyfriends, fathers, and husbands during this time. Things could get UGLY.

Also known as man-cycle.
Tom was such a brat last night. He must be manstruating.
by Manduh420 June 15, 2007
 
4.
Like a female period (or menstuating) but when it occurs in a man, and he becomes bitchy, annoying and changes his mood every 20 seconds
Lewis went off in another strop, he's completely manstruating
by Jackie Bennet February 05, 2009
 
5.
When a man is "on the rag."
"I think Chad must be manstruating again. He was being a real dick last night.
by Hophead July 10, 2008
 
6.
When a guy gets really hormonal and PMS-y. They get random mood swings. It comes more often than once a month.
John was very moody Saturday. He must have been manstruating.
by 4564315 May 15, 2011
 
7.
anytime a man is acting like a girl i.e emotional, irrational, etc.. its is said that they are manstruating
dude did you see dan?!! he was watching the notebook and started crying, he must be manstruating.
by nicas4life July 05, 2008