When you have a sudden increase in blood flow to the penis from sexually arousing scenarios which causes the penis to puncture a hole through the article of clothing in which the stiffy is concealed.
Pop a stiffy mate.
by Chode Buster April 29, 2011
Get the Pop a stiffy mug.
A way of stating that the male penis is soon to ejaculate. Otherwise known as a boner.
I Pop a Stiffy everytime I get to walk behind Payton
by Blevinz11z March 2, 2012
Get the Pop a Stiffy mug.