This is a thought I've had since high school and I'm kinda shocked that I've never shared it here before:
One metric for whether or not you're really friends with someone is asking yourself if you've pooped at their home.
Caveat: there are some people that will pretty much only poop at their own home. But for me, this is a revealing test.
Most people I'm close with, I've pooped at their home. It's rare that someone is a casual acquaintance and you've pooped at their home. Also, causality and correspondence not being the same thing, etc. Anyway. You're not friends with them because you pooped at their home. But try it out, do a little mental geography, or when you're at someone's home, think about how close you are with them and whether or not you've pooped there. Extra friend points for having pooped at multiple incarnations of someone's home. Also, think about which friends of yours have and haven't pooped in your home.