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6.
The extremely large protruberence which preceeds an "Evil Fat Man" upon entering a room, attempting a menage a trois, or just generally walking around.

See also, Beer Gut, Dunlop Disease, or Spare Tire.
"Damn, did you see the Dorsal Fin on that Evil Fat Man?!?"
by T&E August 16, 2005
 
1.
When you extend your elbow so that it resembles the upper fin of a dolphin, or shark and jam it into your victims back, or scrotum. Mostly done by bullys and neighborhood thugs.
Bully: " I gave this ladythug a dorsal fin and her spine almost cracked."

Thug: " Oh yeah, well I dorsal finned this guys scrotum so hard that his testes fell out."
by Ebony Scrotum January 21, 2012
 
2.
A person who lacks the common sense to participate in any civilized conversation whatsoever but their failure to do so is tremendously hilarious. This is the person that is involved in your group for the sole purpose to get made fun of on a regular basis.

Horniest person in your group

Completely brain dead individual

Sassy to the point of hilarity

To be honest this person is just so stupid that he/she thinks that dorsal fin could possibly be an insult. I mean seriously, dolphins are one of the smartest animals that we know of today. How could anything remotely involving a dolphin be an insult?
Paris Hilton is such a Dorsal Fin.
by Sasquatch1987 September 13, 2009
 
3.
The act of putting multiple strap ons on your back, lying down, and having multiple people ride said strap ons, whilst vigorously doing the worm.
Mickey and some of his friends are trying the dorsal fin tonight.
by Alpha Wolf 13th Brigade May 11, 2013
 
4.
when a person is born with both male and female reproductive parts, but the male part slightly sticks out of the female part
hey that chick has a dorsal fin!!!
ewh nasty!!!
by ashleyyesterhasadorsalfin June 05, 2009
 
5.
The fin on the back (dorsal) side of an aquatic animal such as a fish, dolphin, or shark.
The dorsal fin on that shark is hook shaped
by mimi June 13, 2003