Along with the whole 'Mary Sue' thing where you accuse a character of being a Sue just because you don't like her, PLEASE FOR THE LOVE OF GOD STOP ACCUSING ALL RELATIONSHIPS OF BEING INSTA-LOVE.
Finding someone attractive is not insta-love.
Fancying the pants off someone is not insta-love.
Having a crush is not insta-love.
It's not love unless they say it is, and even then, use your friggin noggin to figure out whether the character really is in love or just crushing.
Remember crushing? Remember that cute girl or boy in high school you were so desperately 'in love with'? THAT is teenage emotion. Everything is higher stakes when you're a teenager, so a crush feels like love.
Yes, there are a few notorious books out there with insta-love in them. But not ALL YA romances are insta-love.
Stop dismissing relationships because you can't think of a more valid criticism than 'insta-love.'