... "I'm to blame, but I don't even know what I did" ...: D We don't know anything about it - but to apologize for what you didn't do - it's pointless - to apologize for something and not know what - it's just a little less nonsense. If you really provoked an argument, but you don't know "what", apologize to him in general. But it would be best to talk - so you know what he or she is to blame for - so you can avoid it next time.