In blitz chess both the legality and ethics of KxK has long been debated. Of course under recent rule changes KxK now does not happen, but moving the king next to your opponents king and hoping they don't notice still can.
This was exactly the situation that occurred during the Doeberl Blitz on Saturday night, and having made a pretty clear ruling, I felt it important enough to share.
In the game in question the player with the White pieces was winning over the board, having run a passed pawn down to the 7th rank. Both players were short of time (a few seconds for each left) and Black had not chased the pawn with his king, but had kept in the middle of the board. When the White pawn reached the 7th rank, Black moved his king next to his opponents. Not noticing, White promoted, and Black claimed the game.
Due to some clock trouble earlier in the game, this was the last game to finish, and one that I was watching (in case of further clock trouble). Despite Black's claim, I had no hesitation in awarding the game to White. This was for one specific reason, and one general reason. The specific reason was that the Kings standing next to each other was clear evidence that an initial illegal move had been played, and the evidence showed that Black had played it. But, but, but you might say. Doesn't the rules say that White has to claim? And this is where the more general principle comes in. The Laws of Chess are there to protect players who follow the rules, not reward players who break them. In fact this issue was discussed during my time on the FIDE Rules Commision, and my ruling was consistent with that discussion. Again you may ask, why did we not add a rule to cover this situation? Because the Laws of Chess are written on the assumption that players will follow them, not break them. If they had to cover every possible irregularity and potential illegality, then they would be thicker than your phone book.
Of course some people will disagree with my ruling (including the player with the Black pieces) but I hope that it is clear that the ruling was a fair one, in an ethical sense.
(**Update: There is some additional discussion/information about this ruling in the comments section **)