Fifteen to One Scale 

The theory that for every 15 pounds a man puts on, that he loses 1 inch in penis length, due to the increase in the fat pad on the pubic bone.

Fat? That dude's running a minus on the Fifteen to One scale!

Fifteen to One Scale by Squik da Kitty February 20, 2010

fifteenth base 

The act of raping a squirrel.

Dude, my Asian buddy was able to get to fifteenth base yesterday! I tried and couldn't fit.

fifteenth base by thefixer551 November 17, 2009

fifteen second rule 

the rule whereby if a college student is present in his dormitory and takes more than fifteen seconds to answer after a knock, one can assume that he is masturbating.

Bill: Matt, are you there? (knocking)

Matt: Yep, hold on.

(waiting)

(waiting)

(waiting)

Bill: Fifteen second rule, you're officially masturbating. (turns around)
Hey everyone! Matt's masturbating!

fifteen second rule by The Iron Fist January 5, 2009

final fifteen

weight gained in the last year of graduate school as a result of sitting on your ass and writing your thesis/dissertation day after day.

Person A: Has David gained weight? He's looking a little doughy lately.

Person B: Yeah, but it's just the final fifteen. He'll start hitting the gym again after the thesis is finished.

final fifteen by UCDSocGrad November 19, 2011

taking a fifteen 

to take a fifteen minute break in order to masturbate or have quick sexual relations with a partner in a random room.

dude, adam and steve are taking a fifteen in the garage--do not go in there.

taking a fifteen by Brian Bryant October 14, 2008

pen fifteen 

a trick played on girls who are sweet, oblivious, innocent girls. a mean girl will ask them to join the pen club. she says"i'm pen 13, she's pen 14, and we want you to be pen 15. the girl, oblivious as she is, says ok! then the mean girl writes PEN15 or PENIS on the girl's hand.

that girl who played the pen fifteen trick is SO evil!!!!

pen fifteen by chinchilasrule February 14, 2008

Fifteen Minutes 

the amount of time it takes for one to quickly bang someone (usually in a car)

like in the movie grease, "hey putz... 15 minutes!"

Fifteen Minutes by andie September 20, 2003