Vacation is officially over, kiddos. We're back to being old, boring adults with actual responsibilities . We can't say we're surprised, but we're definitely disappointed. Growing up was the biggest scam we ever signed up for, and someone needs to warn the children of the future to avoid making the same mistakes we did. The thing about growing up is that it's inevitable. The adults of Twitter know this harsh truth all too well. Check out the most accurate adulting tweets leading the way into 20…