It is kind of an exaggeration People usually say this to mean that they really ( almost to the point of hatred) don’t want do something with you or be around you Ex. I wouldn’t be your friend if you were the last person on earth Meaning- I do not like you so much that even if I have no friends, it’s better than being friends with you. Let me know if this makes sense

An idiom? Nope. I think everyone is basically right.. but in this movie when he's told that he's the last person on earth it, it actually means he's not "the cheating type". He's a family man. His boss can't believe that he'd be in a situation like that.

it is a saying such as......"I would not marry you even if you were the last person on earth"

Great film. To say someone is the last person on earth means they are someone you never would choose. For example Anthony Joshua would be the last person on earth I'd get into a boxing ring with. Or Theresa May would be the last person on earth I'd pick as a dance teacher.

I think it is a figurative of speech