"Johnny wished mommy loved him; she wouldn't admit it even when Johnny shot her in the arm." -suspense/thriller/horror
"Becoming a memory is something to be thankful for, even if the memory of you makes me cry." -Romance/Drama/Fantasy.
to be quite honest, to make a first opening line of a book work, you need to have a basic story premise to work with so the opening line can be a great starter with great back up.
If you take a look at my suspense/thriller opening line, you could write a story based off that one line, where Johnny only wants love from his mom but only shows her pain and doesn't know it (possible psychological disorder?)
If you truly want to write different opening lines for a book, I suggest for everyone to write "hint fictions", in which is where you write a one sentence line and start getting your mind thinking creatively. Very simple stuff :)