Although laymen call it "bashful bladder", difficulty in public urination is known in medical circles as "avoidant paruresis", or simply 'AP'.
By some accounts afflicting roughly 7% of the population of the United States - or about 17 milliion people, it is the second most common phobia, followed closely by public speaking.
The International Paruresis Association was founded by Professor Steven Soifer, who suffered from AP for about 30 years. After learning how to desensitise himself, he began giving workshops across the United States. He considers it human nature to be embarassed by making noise while eliminating, in particular if other people are present.
The underlying cause of AP is not precisely known at this time, and may be either physiological or psychological, but in general early toilet training is agreed to be at fault.
There seems to be a high degree of correlation between children that are disciplined or embarassed while on the toilet at an early age and the Adult onset of AP. A common theme amoung AP suffers is the parents exhortation to "hurry up and go!", or "if you don't go now you won't be able to go until we reach....".
Soifers desensitzation therapy is practical and, no pun intended, "hands on"; the patient is instructed to "pee wherever you can". He reccomends first urinating in a hotel room, then a mall, zoo, or museum".
He also advocates "group work", but it's not clear to me what exactly this entails.
Sofier believes that personality plays a role; if a child is "intensely sensitive, self-conscious and self-critical", then the probabilty of adult AP is much higher.
He also blames crude restroom design in the US, with bowl-shaped urinals splashing loudly and urine flying back up into the air when men try to "hug" the urinal to gain some privacy.
Sofier notes that AP sufferers travel happily in Europe, which tends to build more small, individual restrooms, featuring "civilized full doors instead of cattle stalls".
But America's rugged individualists are said to shun such niceties, preferring to rub elbows at the trough and compare streams.
He notes that AP is ancient - "In the Middle Ages, armies would curse their enemies with the inability to void," - but the first clinical referenced didn't appear until the early 1920s.
Doctors would diagnose them with 'psychogenic urinary retention' and perform a transurethral resection, widening the bladder neck.
The International Paruresis Association has a web site, http://www.paruresis.com