Or maybe it's a combination of the three.
There's nothing worse than getting on the metro during rush hour, stressing over which individual you are going to choose to be your seat-partner for the next 40 minutes (do you go with slightly creepy businessman who looks like he might fall asleep and trap you next to the window, or do you choose the attractive but oddly-smelling Occupy protestor who just may start a 99% chant in your ear?), committing to the seat, and then realizing, once the person starts laughing hysterically at what appears to be nothing, that he or she may be certifiably insane.
Unfortunately, I have become that person. Not the person who is regretting the decision to ever step on the 5:00 train (believe me, that stage has come and gone. I'm way past the whole "I'm too mature for this laughter" act)- I am the one who is shaking uncontrollably because of the conversation I've just overheard on the platform. Or something I read earlier that day. Or something someone once told me when I was fourteen and I just remembered how funny it was. I no longer have any shame for personal public laughter.
So next time you find yourself scanning the walls for emergency exits because the person next to you is demonstrating signs of mental instability, be careful. Either something hilarious is going on in their head- or you are just really funny looking...
(this picture is a great example. I went into this restaurant, sat down under this picture, and smiled- while my friend stood 30 feet away and captured this moment on camera. Everyone around me wondered why I was smiling at nothing... Do they not realize that Ramses is the bestttt?)