Grasshopper

Every day, Jim gets two six packs on the way home from work. When he gets home, he sits in his living room until they're gone. One day, just as he's getting to the end of the last beer, he hears a knock at the door. He goes to answer it, and sees a six foot tall grasshopper. Before he can say a word, the grasshopper punches him in the face as hard as he's ever been hit! Floored, he can't respond before the grasshopper leaves.
He decides he'd better be in better shape, so the next day he only gets one six pack. Just as he's finishing the last beer, he hears another knock at the door. He gets up to answer it, a bit more wary this time. Not that it does him any good. The six foot tall grasshopper is there again, and this time hits him twice, each one as hard as he's ever been hit! Again, the grasshopper leaves before he can do anything.
On the third day, he decides he'd better just skip his beer. He's sitting in his living room, stone cold sober, when he hears a knock at the door. He checks his peephole. It's the grasshopper. But he figures this time he hasn't been drinking and he can take him, so he opens the door. Before he can do anything, the grasshopper knocks him down and kicks him until he can't move. Again, the grasshopper leaves when it's done.
Obviously he's in bad shape after that, so he goes in to see his doctor. He describes what's been going on. The doctor nods knowingly, "Yeah, there's been a pretty nasty bug going around."