Someone explain the saying "That's so gay"

I never quite understood it.  I just never did.

I grew up in the inner city of New York, so I think it has something to do with my early hyper-awareness of the American socio-economic and racial class structure.  I knew there were different classes of people...mainly poor and rich were the two big ones for me, but as life continued I learned that people can hate you for way more than your money.  I guess I realized sexuality was one of those factors by which people can judge you when I entered high school.  I went to an all boys Catholic High School...so the latent homoerotic behavior was everywhere.  So something popular I always heard was, "That's gay" referring to an object or event, and rarely referring to a man or woman.

Whenever someone accuses someone/something (because all nouns have a sexuality these days), my initial response was "Who cares?"  I had Regents to study for, and could seriously care less that your detention slip is "gay".  I was busy with too much work to care that your detention slip had a curious sexual experiment with an envelope once in college (or maybe they were referring to the teacher who gave them detention...I was never entirely sure).  And I was accused of being gay for several reasons (none of them having to do with my romantic inclinations, relationships, or sexual history).  I remember once retorting to such an accusation "so what if I was?"  This was the proverbial nail on the coffin for my social life in middle school.  By admitting that I **gasp** did not care about the specifics for anyone's sexual orientation including my own, I was weird.  I never understood the connection between something being gay and awful at the same time.  I know several gays who are awful...but I don't think they are awful because they are gay.  They're so awful that I don't like to imagine them having sex with anyone, so they're basically asexual in my mind.   

I just overheard some high schoolers throwing this around on the afterschool subway, and I was just wondering what is with this obsession of their's.  I thought the highschooler of today was different from that of 5 years ago.  I mean in that time we came up with YOLO and SWAG to keep them distracted, didn't we?  Snapbacks and acid wash were revived to give them inspiration to the struggles of old. Meh...I guess I was annoying some other NYC blogger when I was that age.  I kind of wish people would get over it, and read more books, and just behave like they have an education.

I don't understand The Big Bang Theory

I just don't understand the show.  My family watches it religiously so I've been sucked in, but I still catch myself from entering the clan of the devout fans.  I just can't help but realize that none of these people are functioning human beings aside from Leonard and Penny.  Even then...those two characters have such pitiful existences.  Penny is a failing actress who hangs out with people who are so far out of her normal social circle, that she clearly must be SOOOO INDEPENDENT AND QUIRKY.  Leonard is cool though.  He does what he loves, and has normal social anxieties, and an overbearing mother.  He's like me....but with a PhD.

All of these characters are just so socially inept that I feel uncomfortable being around them (except Leonard and Penny).  Howard is just on the verge of being a sexual criminal, Raj is has some sort of mental disease and Sheldon is just a egotisical sociopath.  Sheldon literally does not care about anyone around him...ever.  Not even this cast of people...the only people who love him for whatever reason.  I could understand Leonard wanting to hang around these guys because he grew up with them.  They were his friends for the longest time and so no amount of awkwardness could break their bonds of brotherhood, but that just sucks for Leonard. The one thing I never quite understood was Penny.

Penny is a completely normal, functional, young woman.  Can't she find better friends than these guys and her two "girlfriends" Bernadette and Amy?  These people literally have no social tact and they're so obviously made to be unattractive.  Bernadette is nice but she doesn't get enough time on screen.  I've never known such a hot girl to hang out or sleep with such a crew.  Her ex boyfriends seemed like more fun than this cast.  I just find it highly unrealistic.

Penny...go out and get some better friends and stop sleeping with the faculty of some unknown university.  Broaden your horizons and get some new friends who share common goals and interests so this show can finally make sense. And Leonard...keep doing you.  You're alright by me.  Thanks/