1. You are convinced you’ve become the real life Serena and Blair.
2. You begin to notice each other's OCD tendencies, or lack thereof.
3. You get really comfortable with each other.
4. You make up super discreet gestures to signal approaching foreign hotties.
5. You learn when to give each other space.
6. You support each other more than ever, especially when you’re stumbling drunk through a foreign city.
7. You spend so much time together that you don’t even have to speak to each other. Telepathy takes over.
8. You'll become over-tired and delusional, and cry together at least once. Mostly likely while watching a sappy, overpriced movie on a plane.
9. You contemplate never returning home and running away forever.
10. Your friendship becomes stronger than ever.