That growing realization over time, putting pieces together and harboring and denying suspicions, that the people you're hanging out with aren't actually laughing with you, but at you. Even when you're laughing as well.
The realization that you failed to realize months ago that your life was passing you by, and that you are failing to grab hold of your dreams, or even your vague notions of what you should have for dreams, and that you might actually be stuck in a rut.
That aching lingering feeling you get after you've attempted a joke that wound up hurting someone who you really didn't want to hurt, and they've accepted your apologies and you can't apologize and be forgiven anymore even though you really feel you need it.
That suspicion that she really would have said yes if only you'd actually asked her, rather than pussy-footing around it for three fucking years and never bringing it up, oh god, why didn't you?
That question, in the back of your head, bothering you constantly, wanting to know if the best years of your life really were a half-dozen years ago and might it all be downhill from here.
The thirty seconds when your phone starts to ring, and you look at it, and you see it's someone you want to talk to, but you feel dirty and uninteresting and rather suspect that you won't be all that enjoyable to talk to at the moment, so you wait for it to go to voicemail, daring yourself to pick it up the entire time.
The thirty seconds as you try to call someone after finally realizing you want to talk to them, regardless of how depressing you might be, and it rings and rings and why won't at least the voicemail pick up so you can hear their voice and not leave a message because answering machines bother you in ways you can't quantify.
That gulf in between the beginning of your story and the end of it, when you realize you can't remember how the punchline goes, only that it's funny and that you should really be able to remember it rather than just summarize it, but trying to remember how it was worded exactly means you blank even on the summary, and you just know that you're going to have to end it with, "Well, I guess you had to be there," or by faking a seizure, and you really don't want to hit your head on the floor just because that stupid punchline was too hard to remember.
That dull hunger as you sit and hit refresh on your post, wondering, "Is anyone reading this? Could someone be enjoying this or preparing criticism on this at this very second?"