Well, I play a whole lot of RTS games. In fact, earlier today I was in a 2 and a half hour long game of Wargame: European Escalation where my and a friend destroyed around (rough estimate) 4-500 tanks. Each of those tanks has around a 5 person crew, so about 2 thousand from tanks alone. I'm not even going to count how many MI-24's I destroyed with full crew and troop complement. Yesterday I was playing some Men of War: Assault Squad and I decided that it would be pretty fun if I held off the enemy for as long as I could before I took the last base. I made some massive defensive lines, made sure that their artillery was destroyed, and loaded up all my troops with the proper ammo, then I left my computer running for an hour or so. Managed to rack up 5 thousands enemy casualties with no prisoners taken. So, about 7k in two days, and those aren't even my good days. Add together all that for over 10 years, and that's probably over 3/4ths of a billion kills in RTS games alone. That's not including FPS's and TPS's either.
EDIT: I totally forgot about Empire at War and when I went on my "Death Star everything not Empire" run.