Arma II mod, DayZ, has spawned a ton of abnormally fun rounds, with players partaking in all sorts of activities outside avoiding and killing zombies.
But this one guy who stalks and terrorizes two players might be my favorite so far. He runs around in circles, chases them, and mumbles some really non-sensical, funny-yet-disturbing words at them. In fact, he freaks them out so much that they make a run for it, and decide the only way to deal with the situation is to kill him and rest easy.
Poor guy. Maybe he just had a speech impediment and wanted to make friends.