be careless of
...being late A lot of mistakes are caused by [his being careless.] 很多錯誤是[他不小心]造成的 he is careless > his being...
1.Being a careless fellow,he forgot all about it. 由於生性粗枝大葉,他完全忘了有這件事 2.The train being late,she waited. 火車誤點, 她只好在月臺鵠候
It shoud be "I couldn't be careless" 譯作 我可不能漠不關心 (or隨隨便便的) 但是 I couldn't care less...