I measure how tired I am if I start feeling sorry for cannon fodder in a game, especially guards in Assassin's Creed. No mercy.
But my gut-wrencher is a mission in Mass Effect. There's some little Indian dude on Citadel who just wants his wife's corpse from Eden Prime back, right? So I go talk to some bureaucrat, and he explains that they're using the body to make better weapons against the Geth and that keeping it would save hundreds of lives by extensions. So I do the logical thing, let em' keep the corpse, then tell the husband.
He just breaks down. He starts screaming and crying and begging. When he's done chewing you out, he just walks off with this dejected look, like he's lost absolutely everything. I did the logical thing, but I still felt horrible. So, naturally, I reloaded and got his wife's body back. I'm such a softy sometimes...