n., adj.,(Richard John formally) Incessant masturbator, 'net porn addict, dates ONLY girlie magazines or left/right hand, can get erect at the fleeting glimpse of a woman's cleavage in a TV soap ad or speeding by the other way on a six-lane highway.
Is one REALLY necessary? It's probably YOU reading this. Just look in the mirror. Dick Jack.
A double-dick jack-off is when a guy takes his own dick in his hand and and grasps it along with his JO buddie's cock, and then jacks them both off at the same time -- trying to cum at the same time so they can feel and see the cum-spasms spurt from one another's dicks at the same time.