Well, first, he is apparently not mentioned in the game. There is simply a lawyer character who believes in banning violent video games. Jack Thompson is sure it's a jab at him.
"...the fact that the lawyer, killed on Niko's first mission, would bring up video games, makes it clearly a reference to me..."
Hmmm, you know, come to think of it, I could be mistaken for Mario...maybe I should sue. Come on, Mr. Thompson. Seriously? The fact that the Florida Bar had to impose disciplinary action on you, and that you lost your license to practice law in Alabama says to me you're basically an idiot.
I wasn't planning on buying GTA 4, but now I may do so just so I can play that mission and pretend it's you.