In response to kindnesses I sometimes say "不好意思了" and I don't think there has ever been a misunderstanding. But as an English speaker I feel unsure how this is different from saying "不好意思" for a bad thing. Can anyone advise on how the two meaning differ in use?
Does 了 occur here only in response to a kindness, and not in describing a bad thing?
Let me give an example. A friend took me to see a friend of hers who gave me a thoughtful gift. I said "thank you." Everyone involved spoke enough English but later I thought "thank you" was not the right thing to say. In English I could have said "this is too kind of you," or in Mandarin 不好意思了. My friend confirmed that in her opinion those would have been better. And I normally do say 不好意思了 at times like this.
It was not a case of any problem either with the gift or my gratitude. It was just a case where I should have been more modest. Maybe such things are always clear from context but I wonder if there are points of usage aside from context to distinguish the agreeable sense of 不好意思 from the sense of something wrong.