"Me too!" or "Me neither!"

When do I use "Me too!"?

Use "Me too!" if the opinion is positive and the sentence starts with I, You, He, She, We or They.

Example: Your friend says, “I love rock music!”
You love rock music too, so you can answer with “Me too!”

When do I use "Me neither!"?

Use "Me neither!" if the opinion is negative (look for the words 'do not', 'not' or 'don't') and the sentence starts with I, You, He, She, We or They.

Example: Your friend says, “I don’t like dogs!”
You don’t like dogs, so you can answer with “Me neither!”

Look at this conversation between Jack and Lucy:

Jack: I love geography!
Lucy: Me too – but I don’t like maths.
Jack: Me neither!