Seven With One Blow
I kill flies with a dishtowel.
I grab one corner and roll it up and snap it like you'd do at somebody's butt in a locker room, if you were mean enough to do that to somebody. I wait until they're in a good position. If they keep getting into corners and stuff I flick them half-heartedly with the towel to make them keep moving until they land in a better spot. Wham! Dead flies. And they don't squish either, just drop.
Lately they've just been congregating on the living room window in the late afternoon, though, so they're easy pickings for anyone with a flip-flop.