In Las Venturas during Ken Rosenburgs mission where you go and meet Joey Sendocko. When you enter the room with the big freezer when everyone is shooting at you Ken will run into the freezer, and either before he goes in or after you get him out he will say "hey this is just like old times isn't it Tommy!" to which Carl responds "WHo the f*** is Tommy?" Which is a reference to Tommy Vercetti the main character in Vice City. I must note however Ken dosen't say this every time on the mission. He has said only 1 or 2 times for me.