The sweat that forms on your balls when you're fucking your sister. May also be applied when fucking your hot female cousin, i.e. incest.
The relative humidity went up as soon as mom & dad left for the evening and I slid into my sister.
by Bushpig61 September 03, 2010
The bead of sweat that rolls down your Sister's back when you're banging her doggie style.
The Relative Humidity was high during our Family Union
by Anonymous September 18, 2003
It's that little drop of sweat that beads up on the back of your neck and dribbles down your back, thru your crack and eventually drips off of your ball while your fucking you sister.
by Pat May 14, 2003
The sweat that drips off your balls when you bang your sister-in-law.
"The relative humidity was way high at my cousin's wedding".
by Mysteron August 04, 2003
the saliva left on your genitals after your cousin gives you oral sex
Man last night my cousin trina came over to my house. I just thought we were gonna hang, then a few to many beers. Damn the ho was down on me! ie. relative humidity!
by RD Machine January 10, 2007
The perspiration that forms between the shoulder blades of your first cousin, while you are fucking her in the ass.
Uncle Mike ... the relative humidity sure is high in your daughters bedroom.
by maggotvommit April 17, 2004
The sweat that drips off your balls when you're caught fucking your cousin!
Last night I had some major relative humidity!
by Nicole December 13, 2003