maybe I am imagining things, but I am under the impression that there is an effect for each response. The gentle one, "I'm sorry...", seems to work as the answer to a last warning. For example, I bribe some CS close to another civ, the leader of that civ comes up complaining about it, I choose "I'm sorry...", and everything stays apparently the same. Yet if I go and do it again (bribe another CS inside his sphere of influence), then he gets mad at me for the fact AND for not sticking to my word. The other option, in the same scenario, would mean telling such leader "I will do what I want", meaning he will get immediately mad at you for the fact, but no negative impact for breach of word becasue there was none.
That is how I feel it works (based on the effects I have seen in my interaction with the other leaders), but I have no "xml-based" proof... perhaps somebody dug into the files to confirm/deny this?