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2.
A psychological phenomenon that occurs when a male of the human species witnesses a gorgeously endowed female, and procedes to lose the ability to concentrate or focus on anything except her:

1. Tits
2. Ass
3. Legs
4. Tits
5. Face

In the case of Arkansas natives, may produce confusion about the definition of adultery, and lack of ability to use the word "is"
Man 1:Im sorry, what were we talking about? That blond chick that just walked by..

Man 2: With the knockers? Seems like you just had a case of penile dementia, my friend!

Man 1: Yeah, good thing we are at a titty bar. Lapdances are on me!
by Me February 26, 2003
 
1.
The phenomenon whereby your penis will urinate anywhere but where you're aiming.

Possible causes are sex, sitting uncomfortably, and having a foreskin.
Jerry: Dave, why is the ceiling wet?!
Dave: Sorry, I had penile dementia.
by Locus0mega March 05, 2011
 
3.
Penile dementia is the state of becoming so senile that you forget it is not socially acceptable to grab the asses of strangers.
Sorry about Grandpa. He's suffering from penile dementia.
by Gina Cochina July 15, 2010
 
4.
to be suffering from a priapism, that is a continuous erection of the penis. This ailment is both painful and socially embarrassing.
Trevor was disappointed: he had to miss several West Ham matches because of chronic penile dementia.
by Dunky Oggins November 15, 2003