How do you say "I'm sorry?" I think that in most circumstances, it is best said as, "sumimasen" (すみません) and not "gomen-nasai" (ごめんなさい). Occasionally, when you actually mean to apologize for something you've really done wrong, it is appropriate to say, "sumimasen moushiwakenai-desu" (すみません 申し訳ないです). "Gomen-nasai" sounds, to me, rather intimate, like the kind of thing that is said between parent-child or spouses.
How do you say "I'm sorry?" I think that in most circumstances, it is best said as, "sumimasen" (すみません) and not "gomen-nasai" (ごめんなさい). Occasionally, when you actually mean to apologize for something you've really done wrong, it is appropriate to say, "sumimasen moushiwakenai-desu" (すみません 申し訳ないです). "Gomen-nasai" sounds, to me, rather intimate, like the kind of thing that is said between parent-child or spouses.