Dom speaks:
As a sidenote, do any of you have any idea how hard it is to do stick figures in Photoshop with a trackball?

"Shirt Guy Dom" is a reference to "Shirt Guy Tom" from Sluggy Freelance, who is also known for stick figures.

Dom speaks:
It's from Sluggy.

The Shirt Guy Dom strips later began invading other web comics:
SGD at Strange Candy
SGD at Exploitation Now
SGD at Real Life
SGD at Real Life #2
SGD at Little Gamers