Way 1 · best default
I'm really sorry
A clear, sincere apology. "Really" shows you mean it. Fine with anyone, for most mistakes.
Examples
I'm really sorry, I didn't see you there.
I'm really sorry about yesterday. I was in a terrible mood.
In a conversation
A: Ow, that was my foot!
B: Oh no, I'm really sorry. Are you OK?
Common mistake
Not: My bad, I deleted the client's file.
Say: I'm really sorry, I deleted the client's file.
"My bad" is for tiny slips with friends. For a real problem at work, it sounds like you don't care.
