When you have a boner in a situation that is not conducive to boners and you are forced to furtively reach down and tuck your wanger upwards, against the waistline of your pants. The resulting protrusion of the head is known as a "pilbo".
Man, I got the weirdest boner in chem today. I tried to wait it out, but when the bell rang, I had to cut my loses and rock a pilbo.
by hambronius jones August 05, 2010