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1.
A male platonic companion that a young, attractive woman keeps around to feel better about herself. The Dick in a Jar is stable, friendly, sensitive and nonthreatening. He is infatuated with her, but she sees him as a brother -- a brother with whom she cuddles while watching movies and complaining about the latest alpha male to break her heart. The Dick in a Jar secretly awaits his female companion's revelation that emotionally abusive fucktards will never make her happy and that he is actually the man of her dreams, but he waits in vain.
Mark: So, what's up with your roommate and that dorky guy who always spends the night? Are they bumpin' uglies?

Shauna: Naah, he's just her Dick in a Jar.
by Pavlov's Cat January 31, 2011
 
2.
when a male is completely controlled by his girlfriend/woman/significant other, and constantly bails on his friends to be with her.
Person 1: Dude, Marco is being such a dick in a jar. I haven't seen him in months.

Person 2: What the fuck is a dick in a jar?
by MooseLLama June 06, 2009