could "I hate you" ever mean the opposite?

You have to care about someone to actually hate them. I wouldn't call that love though.

If you surprise someone with a gift they really wanted, but you had led them to believe you didn't get them. They could say it then but laughing, and mean the opposite!

I think to be able say that jokingly would mean you and that person have already shown that they actually love eachother

Yes, people sometimes say strong things when they're very emotionally invested.

sometimes, but in most of my cases it definitely does not

It's a passion at the very least but no, not love

Yes

yeah if feelings are involved

people say love and hate are similar emotions.

nope.

I just responded to a guy's story where he told a girl he hated her, just so she'd move on.

Hate is a look. At the very most. Not words.

It can in anime

Never when I've said it.