short for 'Massive Sperm Buildup' - usually occours in young male adults under 25 as a result of no sexual activity for more than a week or 2
Derek had not masturbated for about 3 weeks and was suffering from a severe case of MSB, but after watching 5 minutes of crazy cumshots #4 he had a massive sperm bomb and had to use his blue bandanna to clean up!
by Cam Bomb February 19, 2012
21 more definitions
Top Definition
Abbreviation for "massive sperm buildup", often incurred after a long sexual drought; common malady among geeks
<dumpee> duder, ever since she left me, I've had some serious MSB going on
by grasshoppers January 20, 2003
middle school bitch. one that wears excessive amounts of abercrombie apparel, attains a facebook around age 12, and always seems to have a new series of naked pictures out. Identifying an msb: prefers to straighten her hair, owns some sort of coach bag, says things like "loves it" and AlTeRnAtEs CaPiTaLiZiNg LeTtErS wHeN sHe tYpEs. like so (the written msb language also often includes numerous asterisks, hearts, and exclamation points.) <33 :)

"That msb sent me pics last night, so I sent 'em to everyone I know."
by caitymoomattyshu December 03, 2008
Stands for Mother Sister Black. A woman that is african-american, has children and is known to a guy as his buddy's sister would classify as an MSB. Most white men have an 'achivement sex list' which includes a mom, a black girl, somebody's sister, a teacher, etc... If a white guy has sex with an MSB it is considered a powerful achievement.
Duder 1: "I can't believe you fucked Garrett's sister. She's half black and has a kid dude. You totally scored an MSB!"

Duder 2: "I know man, it was pretty amazing. Those titties were so nice."

Duder 1: "Damn! You're so far ahead of me now. All you have left on your list is a teacher. I got a lot of catching up to do."
by westfalia December 22, 2009
A very hot teacher. Every kid wants to fuck her and thinks she is a bit naughty.
Damn dude did you see Ms. B last night? I wanted to give her a portugese breakfast she was so hot!
by Mandingo Wheaton March 15, 2009
Mother Sons of Bitches; person or persons placing constraints on actions of others; "The Man"
Persons are not permitted on the boat canopy, by order of the MSB
by nobodycomplain May 08, 2011
Massive Sperm Buildup: suffered by males only; very similar symptoms to a female's PMS.

When a man hasn't been able to bust a nut in a while and thus becomes cranky, bitchy, whiney and down right intolerable.
I wish he would get laid already so he can relieve his MSB because I'm tired of his whiney-ass bitching!
by Thai Chivette July 19, 2014
Making Shit Blacker - Paving term used by companies employees in reference to the color of asphalt. See "Pave The Earth".
Damn, Bubba we making ship blacker today (MSB).
by Druncle April 28, 2009

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