The phenomenon where, in colder winter months, vasoconstriction leads to an average of 30% less girth in the male genitalia. This is due to the body trying to conserve heat, thereby shutting down certain blood pathways to stay warm; the penis being one of them...
Guy 1: Polar vortex hit this week, and I swear my dick shrunk like a half inch in diameter. I don't even want to show my girlfriend...
Shy Penis is a term used to describe a general state of shock exhibited by one's penis in the presence of other men, most particularly when attempting to urinate.
Ted stands by the urinal and pops it out just as Ralph walks into the bathroom. Ted waits and waits and waits, but is unable to force the pee out.