迟到五分钟、轻轻碰到别人，说“不好意思”通常够了；真的造成麻烦，比如弄坏东西、发错重要文件，可以说“对不起”。
For being late by five minutes or lightly bumping into someone, saying 'excuse me' is usually enough; if you cause real trouble, like breaking something or sending the wrong important document, you should say 'I'm sorry'