The physical and emotional relief a man feels after orgasm when he's been aroused or deprived of sexual satisfaction for an extended period of time. This condition is also known as "Blue Balls".
Stiffy Relief can be achieved by masturbation or with a sexual partner.
Stiffy Relief has been achieved when the penis is limp, shriveled and it's owner is smiling :)
"Oh Baby, I'm aching, how about some stiffy relief?"
"Dude, she may not be the sharpest tool in the shed but she's the best at providing great stiffy relief."
"Obviously the fool was thinkin' that buying me a beer was enough to qualify him for some stiffy relief!"