porch dog 

A person who frequently attacks others in speech or writing, but who poses no intellectual threat whatsoever. The motivation of this type of person can usually be accurately construed as a desire to be obnoxious and offensive.

Origin: The phrase "porch dog" is used to refer to dogs that sit on front porches and bark (vigorously and fruitlessly) at passersby, but who pose no physical threat.

Yeah, that guy has a scathing response to just about everyone who posts in this forum. He's a real porch dog.

porch dog by Vitruvian Man May 25, 2006

porch dog 

Someone who is very lazy, especially at their work place.

"That porch dog is so lazy he won't even lick his own butt!"

porch dog by Guy O November 1, 2015

dog perch

a beer belly

Have you seen the size of that bloke's dog perch?

dog perch by Boothenangel September 27, 2003