Yes, I've griefed. My rules are just "no cheating, no flaming." In EVE Online I've went to war with countless miners and PvEer's just because I could. I've ransomed ships for hundreds of millions of ISK, and killed them anyway after they paid. I've joined a small group of people, got lent a logistics ship, then helped them kill people who were friendly to my corporation, before stealing the ship they gave me. I've joined peoples corporations and pretended to be their friend just to get a chance to kill and steal from them. I could go on.
Outside of EVE? A few minor things, nothing noteworthy.
Do I apologise? Why would I do that? At the end of the day, it is just a game. Everything I do is perfectly acceptable within the game mechanics and it's damn well fun. When I annoy people it's a bonus, because I don't annoy people, I annoy people who take the game too seriously.