Reader Willkiller tipped us to this WTF?!-thread in the Gametrailers forum. In GTA IV multiplayer, apparently someone's turned into a zombie wearing nothing but yellow Rockstar-logo underpants.
There are a few comments indicating gamers have seen zombies in online play, but nothing about transforming into one yet. Theories range from getting killed by a Rockstar employee, to killing a Rockstar employee, to getting the highest ranking.
They quote the official strategy guide (I don't have it) "If you see unclothed characters, look out! Only players who have reached the max ranking of 10 and a few other "special" people get the honour of shooting in their skivvies." But this player says he's only at Level 2. The user's name in the forums is GTA. I couldn't find a PSN ID for him.
More pictures after the jump. Warning, one's at a kinda uncomfortable low angle.
Zombie in Yellow Underpants [Gametrailers forum, thanks Willkiller]