an enormous penis with lots of shaft hair. often mistaken for the trunk of a woolly mammoth.
(2 guys is a locker room)

Guy 1: hey bro, why is your left leg so much harrier than your right leg?

Guy 2: dude, you are seein it from a bad angle. thats not my left leg. its my third leg.

Guy 1: whoa! thats a mastadon!
by leftlanecruzer April 23, 2011
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A nickname describing a midget with an extremely large penis.
Girl 1: Hey you know peter?
Girl 2: Which one? The midget?
Girl 1: Yeah.
Girl 2: What about him?
Girl 1: He's a mastadon.
Girl 2: No Way!
by JannetTheBeast! May 30, 2008
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Something excessively large. To the point that only an abnormal word can affectively describe it.
That guys cock was mastadonic on proportion to his body!
by L. Roman July 14, 2006
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dual fisting: a sexual move consisting of the insertion of one of the males fists into each of the females holes (anus and vagina)
jamaal: dude your hands smell like shit
guunter: yea man, its cause i pulled the mastadon on susie last night
by team mastadon January 08, 2005
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A) A prehistoric wooly-mammoth.

B) One who is simular to the beast in both fur and attitude.
Bob: Hey Jerry, is that a yeti I spy?

Jerry: Bob, I can indeed see how you could be mistaken, but thats just Geoff, the local mastadon.
by F Of J January 08, 2010
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a sexual move that is often considered the most awesomely brutal way to pleasure your woman. First, you have her turn around and bend over as you back away a good 20-30 fists. Then, you make a tight fist with your thumb on the inside (you'll find out why shortly). Then, you ram at her full speed, shoving your fist straight up her vagina, while crying out "MASTADON!!".
I just gave that chick the mastadon from 40 fists away!
by Jimmy Jonga November 27, 2006
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a master of the art of anal sex usually working with a ginormous unit
hes known around the ladies as a regular "Anal Mastadon"
by z man March 10, 2005
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