Have you ever been sitting in a public place--like a coffee shop, somewhere where it's fairly quiet--and someone laughs out loud? I don't mean with their group of friends, I mean just alone while they're reading. I have no problem laughing by myself but I can't stand when people self-consciously laugh out loud like, "Oh look I'm having fun AND I have a sense of humor HAHAHA).
A particularly obnoxious example of this is if you're on the subway and someone's reading a book---NO: The New Yorker--and they give this little laugh so that you know they are fucking smart and they "get" the joke. The thing is that most things don't necessarily even warrant this vocal outreach. Or they'll be reading something that obviously isn't universally hysterical, like, I don't know, The Economist, but they give a little "Ha" because they are fucking on the "in" and they know a funny markets joke when they see one.
Sometimes I'll be sitting with a group of friends and we're all doing our own thing (pretending to work) and then someone will check their email and laugh out loud. It's not like a loud laugh, it's like a knowing chuckle.
Cool friend : Haha
Me the loser: What's so funny?
MtL: Cool friend, WHAT'S SO FUNNY
(CF leans into computer screen a bit, leans back in chair still looking SUPER engaged, looks over)
CF: Sorry what?
MtL: What's so funny
CF: Oh, it's nothing. Ha
Sometimes they'll even add in a "Oh, it's nothing. This really hot guy (insert name) is just so ridiculous." Ooooh, okay, well then I obviously wouldn't get it.