According to Wikipedia:
"Paruresis (pronounced /pærjəˈriːsɪs/), also known as pee shyness, shy kidney, bashful bladder, stage fright, urophobia, shy cock or shy bladder syndrome, is a type of phobia in which the sufferer is unable to urinate in the (real or imaginary) presence of others, such as in a public restroom. It can affect both males and females. The analogous condition that affects bowel movement is called parcopresis."
So that basically means that the guy in question is rumored to not be able to urinate while knowing that there are people around, unless it's some sort of slang I'm not familiar with. 😛