disussion from other thread....
In addition to sexual arousal, erection in males can be caused by mechanical stimulation, or by the pressure of the filled urinary bladder. Erections when waking up are common, most likely due to a full bladder.
Piss-proud is an idiom that refers to the common phenomenon of a man waking in the morning with an erect penis.
It is attributed normally as the result of either a) a full bladder (e.g., Oxford English Dictionary) or b) sexual dreams (e.g., Der Pinsel der Liebe. Leben und Werk des Penis by Bo Coolsaet (1999)).
However, both of the above purported explanations are flawed, since a) a full bladder during a wakeful state (fortunately) doesn't cause an erection, unless heightened by additional stimulations such as a bumpy buss ride, b) piss proudness usually is not associated with sexual dreams.
A possible explanation of this familiar condition might be that it is a result of a full bladder during the relaxed physiological state of the male body during sleep.
both from wikipedia
"HAVE YOU EVER GOTTEN A BONER?????"
"NO, IM HOPING TO GET ONE FOR CHRISTMAS THOUGH"
-ROBIN WILLIAMS FROM THE MOVIE JACK.
I just wet my bed to avoid this problem
The worst was in junior golf tournaments when I would be in a hotel with someone and they would be like k get in the shower we gotta go... I just laid under the blankets and was like, uhhh... yeah...