YOU SAID:

It hadn't been impossible not to laught at him a week ago

INTO JAPANESE

一週間前に彼を笑わないことは不可能ではなかった

BACK INTO ENGLISH

It wasn't impossible not to laugh at him a week ago

INTO JAPANESE

一週間前に彼を笑わないことは不可能ではありませんでした

BACK INTO ENGLISH

It wasn't impossible not to laugh at him a week ago