"If I was mean to you I'm sorry"
This is a perfectly understandable and natural sentence to my mind.
But can you tell me what kind of conditional we're dealing with here? And also: would British English prefer "have been" instead of "was"?
One more: Is it possible to have this sentence:
"If I had been mean before the party then I'm sorry".
Here the speaker wants use the past perfect construction. He might want to do that if he wished to defend himself by restricting his meanness to prior to the party, thus, e.g. opposing the other person's claim that he had been mean the entire day, including the party.
Edit: Indeed, I had forgotten about non-contingent "ifs", thanks for pointing to this phenomenon. I think, after reading the responses, more strongly that there is no room for the "had been" case in English, unless aiming for some sort of markedness.